DEVELOPING INNOVATIVE SYSTEMS FOR REINFORCED MASONRY WALLS COOP-CT-2005 CONTRACT N. 018120 Design of masonry walls D6.2 Page 1 of 106 Deliverable 6.2 Guidelines on the design for end-users Due date: July 2007 Draft submission: July 2007 Final submission date: January 2008 Issued by: TUM WORKPACKAGE 6: Design of masonry walls (Leader: TUM) PROJECT N°: COOP-CT-2005-018120 ACRONYM: DISWall TITLE: Developing Innovative Systems for Reinforced Masonry Walls COORDINATOR: Università di Padova (Italy) START DATE: 16 January 2006 DURATION: 24 months INSTRUMENT: Co-operative Research Project THEMATIC PRIORITY: Horizontal Research activities involving SMEs -50 0 50 100 150 200 250 300 120 150 180 210 240 ρ v = 0,037% ρ v = 0,049% ρ v = 0,070% ρ v = 0,086% Shear (kN) Moment (kNm) M-N domain for walls of different length and fixed vertical reinforcement (spacing 780 mm) Tension Compression Limit 2-3 Limit 3-4 Limit 4-5 Limit 5-6 Limit 6 0 50 100 150 200 250 300 350 -10000 -8000 -6000 -4000 -2000 0 2000 4000 NRd (kN) MRd (kNm) l=1165 mm l=1945 mm l=2725 mm l=3505 mm l=4285 mm l=5065 mm l=5845 mm l=6625 mm l=7405 mm Vd (Md/Nd) [kN] -5000 -4000 -3000 -2000 -1000 0 1000 0 200 400 600 800 1000 1200 1400 1600 Md [kNm] N d [kN] 0 30 60 90 120 150 180 210 240 270 Loadings V-M domain (left); M-N domain (middle); V (M-N) domain for concrete, perforated clay and hollow clay unit reinforced masonry Dissemination level: PU Rev: FINAL
106
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Transcript
DEVELOPING INNOVATIVE SYSTEMS
FOR REINFORCED MASONRY WALLS
COOP-CT-2005
CONTRACT N 018120
Design of masonry walls D62 Page 1 of 106
Deliverable 62
Guidelines on the design for end-users
Due date July 2007 Draft submission July 2007
Final submission date January 2008 Issued by TUM
WORKPACKAGE 6 Design of masonry walls (Leader TUM)
PROJECT Ndeg COOP-CT-2005-018120
ACRONYM DISWall
TITLE Developing Innovative Systems for Reinforced Masonry Walls
COORDINATOR Universitagrave di Padova (Italy)
START DATE 16 January 2006 DURATION 24 months
INSTRUMENT Co-operative Research Project
THEMATIC PRIORITY Horizontal Research activities involving SMEs
-50 0 50 100 150 200 250 300
120
150
180
210
240
ρv = 0037 ρv = 0049 ρv = 0070 ρv = 0086
Shea
r (kN
)
Moment (kNm)
M-N domain for walls of different length and fixed vertical reinforcement (spacing 780 mm)
TensionCompression
Limit 2-3
Limit 3-4
Limit 4-5
Limit 5-6
Limit 60
50
100
150
200
250
300
350
-10000 -8000 -6000 -4000 -2000 0 2000 4000
NRd (kN)
MRd (kNm)
l=1165 mml=1945 mml=2725 mml=3505 mml=4285 mml=5065 mml=5845 mml=6625 mml=7405 mm
Vd (MdNd) [kN]-5000
-4000
-3000
-2000
-1000
0
1000
0 200 400 600 800 1000 1200 1400 1600
Md [kNm]
Nd
[kN
]
0 30 60
90 120 150
180 210 240
270 Loadings
V-M domain (left) M-N domain (middle) V (M-N) domain for concrete perforated clay and hollow clay unit
reinforced masonry
Dissemination level PU Rev FINAL
Design of masonry walls D62 Page 2 of 106
INDEX
INDEX 2 1 INTRODUCTION 5
11 DESCRIPTION AND OBJECTIVES OF THE WORK PACKAGE 5 12 OBJECTIVES AND STRUCTURE OF THE DELIVERABLE 5
2 TYPES OF CONSTRUCTION 6 21 RESIDENTIAL BUILDINGS 6 22 SERVICE COMMERCIAL AND INDUSTRIAL BUILDINGS 7
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS 10 31 PERFORATED CLAY UNITS 10
311 Perforated clay units for in-plane masonry walls 10 312 Perforated clay units for out-of-plane masonry walls 11
32 HOLLOW CLAY UNITS 12 33 CONCRETE MASONRY UNITS 14
4 GENERAL DESIGN ASPECTS 16 41 LOADING CONDITIONS 16
411 Vertical loading 16 412 Wind loading 18 413 Earthquake loading 19 414 Ultimate limit states load combinations and partial safety factors 22 415 Loading conditions in different National Codes 25
43 MECHANISM OF LOAD TRANSMISSION 31 431 Vertical loading 31 432 Horizontal loading 31 433 Effect of openings 32
5 DESIGN OF WALLS FOR VERTICAL LOADING 34 51 INTRODUCTION 34 52 PERFORATED CLAY UNITS 35
521 Geometry and boundary conditions 35 522 Material properties 39 523 Design for vertical loading 41 524 Design charts 42
Design of masonry walls D62 Page 3 of 106
53 HOLLOW CLAY UNITS 44 531 Geometry and boundary conditions 44 532 Material properties 45 534 Design for vertical loading 52 534 Design charts 53
54 CONCRETE MASONRY UNITS 54 541 Geometry and boundary conditions 54 542 Material properties 55 543 Design for vertical loading 55 544 Design charts 56
6 DESIGN OF WALLS FOR IN-PLANE LOADING 57 61 INTRODUCTION 57 62 PERFORATED CLAY UNITS 59
621 Geometry and boundary conditions 59 622 Material properties 59 623 In-plane wall design 60 624 Design charts 63
63 HOLLOW CLAY UNITS 68 631 Geometry and boundary conditions 68 632 Material properties 69 633 In-plane wall design 69 634 Design charts 71
64 CONCRETE MASONRY UNITS 78 641 Geometry and boundary conditions 78 642 Material properties 80 643 In-plane wall design 81 644 Design charts 83
7 DESIGN OF WALLS FOR OUT-OF-PLANE LOADING 87 71 INTRODUCTION 87 72 PERFORATED CLAY UNITS 87
721 Geometry and boundary conditions 87 722 Material properties 88 723 Out of plane wall design 88 724 Design charts 91
73 HOLLOW CLAY UNITS 93 731 Geometry and boundary conditions 93 732 Material properties 93 733 Out of plane wall design 94 734 Design charts 95
Design of masonry walls D62 Page 4 of 106
74 CONCRETE MASONRY UNITS 97 741 Geometry and boundary conditions 97 742 Material properties 97 743 Out-of-plane wall design 98 744 Design charts 98
8 OTHER DESIGN ASPECTS 101 81 DURABILITY 101 82 SERVICEABILITY LIMIT STATE 101
REFERENCES 103 ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE 105
Design of masonry walls D62 Page 5 of 106
1 INTRODUCTION
11 DESCRIPTION AND OBJECTIVES OF THE WORK PACKAGE
The major aim of DISWall project is the proposal of innovative systems for reinforced masonry walls The
validation of the feasibility of the systems as a whole to be used as an industrialized solution involves the
study of the technical economical and mechanical performance The WP3 WP4 WP5 are devoted to this
studies by means of design and production of materials development and construction of reinforced
masonry systems and by means of experimental and numerical simulations The workpackage 6 is aimed at
producing guidelines for end users and practitioners regarding the design of masonry walls with vertical and
horizontal reinforcement including design charts and a software code for the design of masonry walls made
with the proposed construction systems These products of the WP6 are of crucial importance to ensure the
commercial expansion and the exploitation of the intended technology as they provide the potential users
(designer architects and engineers and construction companies) with understandable easy to use and
sound design tools These rules and tools should provide the average user with easy criteria to safely design
masonry walls for most of the expected situations Moreover the interaction and the incorporation of these
recommendations into norms and codes (eg EC6 and EC8) can vanish any mistrust and strongly foster the
use of the intended structural solutions For special cases the designer will be addressed to scientific and
technical reports and the use of more complex software The workpackage 6 is mainly based on the
experience of WP5 through which the understanding of the behaviour of reinforced masonry walls under
service and ultimate conditions subjected to diverse possible actions has been gained
12 OBJECTIVES AND STRUCTURE OF THE DELIVERABLE
These guidelines give general recommendations for the structural design of reinforced masonry walls
They cover the main aspects related to how to calculate and design masonry walls built with perforated clay
units hollow clay units and concrete units and also include design charts They are not intended to cover any
other type of reinforced masonry besides those above mentioned and any other aspect of design such as
acoustic thermal etc The aspect related to the construction are covered by D75
The recommendations in these guidelines are based on literature research and code recommendations and
on the experience gained through the testing and modelling of masonry wall specimens in the framework of
the DISWall project They are intended in particular for those end-users (architects engineers construction
companies etc) that are involved with the conception and the design of the buildings
The guidelines are structured into seven main sections After the introduction there is a short reference to
the type of buildings that can be built with the proposed construction systems and a description of the
systems Following some general aspects of the structural design are reported and the aspects of design
for in-plane and out-of-plane loadings are described Other design aspects related to the structural
performance of the buildings are briefly described Finally some reference publications and relevant
standards are listed
Design of masonry walls D62 Page 6 of 106
2 TYPES OF CONSTRUCTION
Some typical example of buildings that can be built with the proposed reinforced masonry systems is given in
the deliverable D75 section 8 In the following the different building typologies are divided according to the
typical structural behaviour that can be recognized for each of them
21 RESIDENTIAL BUILDINGS
The common form of residential construction in Europe varies from the single occupancy house (Figure 1)
one or two-storey high to the multiple-occupancy residential buildings of load bearing masonry which are
commonly constituted by two or three-storey when they are built of unreinforced masonry but can reach
relevant height (five-storey or more) when they are built with reinforced masonry (Figure 2) Intermediate
types of buildings include two-storey semi-detached two-family houses (Figure 3) or attached row houses
(Figure 4) In these buildings the masonry walls carry the gravity loads and they usually support concrete
floor slabs and roofs which are characterized by adequate in-plane stiffness The inter-storey height is
generally low around 270 m
Figure 1 One-family house in San Gregorio
nelle Alpi (BL Italy) Figure 2 Residential complex in Colle Aperto
(MN Italy)
Figure 3 Two-family house in Peron di Sedico
(BL Italy) Figure 4 Eight row houses in Alberi di Vigatto
(PR Italy)
In these structures the masonry walls must provide the resistance to horizontal in-plane (shear) forces with
the floor and roof acting as diaphragms to distribute forces to the walls Very often the lateral (out-of-plane)
Design of masonry walls D62 Page 7 of 106
forces from wind are taken into account in the design by calculating the correspondent eccentricity in the
vertical forces and by reducing accordingly the compression strength of masonry in the vertical load
verifications or can be carryed out directly out-of-plane bending moment verification in the case of
reinforced masonry In case of stiff floors and roofs the out-of-plane verifications for the load bearing walls is
generally carried out separately in the hypothesis of double hinges at the wall bottom and top by comparing
the resisting out-of-plane bending moment with the design bending moment However the in-plane shear
forces are generally the governing actions where earthquake forces are high
In certain cases in particular for low-rise residential buildings such as single occupancy houses or two-family
houses the roof structures can be made of wooden beams and can be deformable even in new buildings In
these cases or in the upper storeys of multi-storey multiple-occupancy residential buildings wall designs
can be governed by resistance to out-of-plane forces
22 SERVICE COMMERCIAL AND INDUSTRIAL BUILDINGS
In service commercial and industrial buildings where masonry walls also reinforced are used as infill walls
with non-structural function their structural design is usually governed only by the resistance to wind and
earthquake forces as the gravity loads are assumed to be carried by the resisting frames In these buildings
the walls must have sufficient in-plane flexural resistance to span between frame members and other
supports Deflection compatibility between frames and walls has to be taken into account in particular if
these buildings are multi-storey buildings In this case the infill walls have to be verified against out-of-plane
earthquake and wind loading to avoid dangerous felt of material that would not compromise the stability of
the building but would prejudice the safety of people
A particular type of building is constituted by the low-rise commercial and industrial buildings generally one-
storey high made with load bearing reinforced masonry instead of infill walls In this case compared to
residential buildings with the same number of storeys the inter-storey height will be generally quite high
(between 5divide8 m) as the inner space has to be used for production or for activities such as sport activities
etc This solution can be chosen for example as it allows obtaining good indoor environmental conditions
suitable for food processing (Figure 5) or for recreational activities (Figure 6)
In this case it is possible to find both deformable (Figure 7) and stiff (Figure 8) roof structures according to
the construction system chosen by the designer The presence of one or the other will influence the
behaviour of the walls If the roof is stiff the horizontal action is mainly distributed to the in-plane loaded
walls The out-of-plane walls in case of seismic action are mainly loaded by the action coming from their
own mass where the roof can be considered a very stiff elastic restraint and act only for its dead-load If the
building is made with deformable roof this is not able to distribute the horizontal load to the in-plane walls In
this case the out-of-plane forces will be dominant In case of seismic action the walls can be tentatively
considered as cantilevers with a vertical load applied at the top and a horizontal load due to the masses of
both the roof and the wall itself The two resulting static schemes of the reinforced masonry walls are
represented in Figure 9
Design of masonry walls D62 Page 8 of 106
Figure 5 Parmigiano Reggiano factory in Ramiseto (RE Italy) Figure 6 Sport centre in Reggio Emilia (Italy)
Gluelam beams and metallic cover
Precast RC double T-beams
Precast RC shed
Figure 7 Sketch of the three deformable roof typologies
RC slabs with lightening clay units
Composite steel-concrete slabs
Steel beams and collaborating RC slab
Figure 8 Sketch of the three rigid roof typologies
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
43 MECHANISM OF LOAD TRANSMISSION 31 431 Vertical loading 31 432 Horizontal loading 31 433 Effect of openings 32
5 DESIGN OF WALLS FOR VERTICAL LOADING 34 51 INTRODUCTION 34 52 PERFORATED CLAY UNITS 35
521 Geometry and boundary conditions 35 522 Material properties 39 523 Design for vertical loading 41 524 Design charts 42
Design of masonry walls D62 Page 3 of 106
53 HOLLOW CLAY UNITS 44 531 Geometry and boundary conditions 44 532 Material properties 45 534 Design for vertical loading 52 534 Design charts 53
54 CONCRETE MASONRY UNITS 54 541 Geometry and boundary conditions 54 542 Material properties 55 543 Design for vertical loading 55 544 Design charts 56
6 DESIGN OF WALLS FOR IN-PLANE LOADING 57 61 INTRODUCTION 57 62 PERFORATED CLAY UNITS 59
621 Geometry and boundary conditions 59 622 Material properties 59 623 In-plane wall design 60 624 Design charts 63
63 HOLLOW CLAY UNITS 68 631 Geometry and boundary conditions 68 632 Material properties 69 633 In-plane wall design 69 634 Design charts 71
64 CONCRETE MASONRY UNITS 78 641 Geometry and boundary conditions 78 642 Material properties 80 643 In-plane wall design 81 644 Design charts 83
7 DESIGN OF WALLS FOR OUT-OF-PLANE LOADING 87 71 INTRODUCTION 87 72 PERFORATED CLAY UNITS 87
721 Geometry and boundary conditions 87 722 Material properties 88 723 Out of plane wall design 88 724 Design charts 91
73 HOLLOW CLAY UNITS 93 731 Geometry and boundary conditions 93 732 Material properties 93 733 Out of plane wall design 94 734 Design charts 95
Design of masonry walls D62 Page 4 of 106
74 CONCRETE MASONRY UNITS 97 741 Geometry and boundary conditions 97 742 Material properties 97 743 Out-of-plane wall design 98 744 Design charts 98
8 OTHER DESIGN ASPECTS 101 81 DURABILITY 101 82 SERVICEABILITY LIMIT STATE 101
REFERENCES 103 ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE 105
Design of masonry walls D62 Page 5 of 106
1 INTRODUCTION
11 DESCRIPTION AND OBJECTIVES OF THE WORK PACKAGE
The major aim of DISWall project is the proposal of innovative systems for reinforced masonry walls The
validation of the feasibility of the systems as a whole to be used as an industrialized solution involves the
study of the technical economical and mechanical performance The WP3 WP4 WP5 are devoted to this
studies by means of design and production of materials development and construction of reinforced
masonry systems and by means of experimental and numerical simulations The workpackage 6 is aimed at
producing guidelines for end users and practitioners regarding the design of masonry walls with vertical and
horizontal reinforcement including design charts and a software code for the design of masonry walls made
with the proposed construction systems These products of the WP6 are of crucial importance to ensure the
commercial expansion and the exploitation of the intended technology as they provide the potential users
(designer architects and engineers and construction companies) with understandable easy to use and
sound design tools These rules and tools should provide the average user with easy criteria to safely design
masonry walls for most of the expected situations Moreover the interaction and the incorporation of these
recommendations into norms and codes (eg EC6 and EC8) can vanish any mistrust and strongly foster the
use of the intended structural solutions For special cases the designer will be addressed to scientific and
technical reports and the use of more complex software The workpackage 6 is mainly based on the
experience of WP5 through which the understanding of the behaviour of reinforced masonry walls under
service and ultimate conditions subjected to diverse possible actions has been gained
12 OBJECTIVES AND STRUCTURE OF THE DELIVERABLE
These guidelines give general recommendations for the structural design of reinforced masonry walls
They cover the main aspects related to how to calculate and design masonry walls built with perforated clay
units hollow clay units and concrete units and also include design charts They are not intended to cover any
other type of reinforced masonry besides those above mentioned and any other aspect of design such as
acoustic thermal etc The aspect related to the construction are covered by D75
The recommendations in these guidelines are based on literature research and code recommendations and
on the experience gained through the testing and modelling of masonry wall specimens in the framework of
the DISWall project They are intended in particular for those end-users (architects engineers construction
companies etc) that are involved with the conception and the design of the buildings
The guidelines are structured into seven main sections After the introduction there is a short reference to
the type of buildings that can be built with the proposed construction systems and a description of the
systems Following some general aspects of the structural design are reported and the aspects of design
for in-plane and out-of-plane loadings are described Other design aspects related to the structural
performance of the buildings are briefly described Finally some reference publications and relevant
standards are listed
Design of masonry walls D62 Page 6 of 106
2 TYPES OF CONSTRUCTION
Some typical example of buildings that can be built with the proposed reinforced masonry systems is given in
the deliverable D75 section 8 In the following the different building typologies are divided according to the
typical structural behaviour that can be recognized for each of them
21 RESIDENTIAL BUILDINGS
The common form of residential construction in Europe varies from the single occupancy house (Figure 1)
one or two-storey high to the multiple-occupancy residential buildings of load bearing masonry which are
commonly constituted by two or three-storey when they are built of unreinforced masonry but can reach
relevant height (five-storey or more) when they are built with reinforced masonry (Figure 2) Intermediate
types of buildings include two-storey semi-detached two-family houses (Figure 3) or attached row houses
(Figure 4) In these buildings the masonry walls carry the gravity loads and they usually support concrete
floor slabs and roofs which are characterized by adequate in-plane stiffness The inter-storey height is
generally low around 270 m
Figure 1 One-family house in San Gregorio
nelle Alpi (BL Italy) Figure 2 Residential complex in Colle Aperto
(MN Italy)
Figure 3 Two-family house in Peron di Sedico
(BL Italy) Figure 4 Eight row houses in Alberi di Vigatto
(PR Italy)
In these structures the masonry walls must provide the resistance to horizontal in-plane (shear) forces with
the floor and roof acting as diaphragms to distribute forces to the walls Very often the lateral (out-of-plane)
Design of masonry walls D62 Page 7 of 106
forces from wind are taken into account in the design by calculating the correspondent eccentricity in the
vertical forces and by reducing accordingly the compression strength of masonry in the vertical load
verifications or can be carryed out directly out-of-plane bending moment verification in the case of
reinforced masonry In case of stiff floors and roofs the out-of-plane verifications for the load bearing walls is
generally carried out separately in the hypothesis of double hinges at the wall bottom and top by comparing
the resisting out-of-plane bending moment with the design bending moment However the in-plane shear
forces are generally the governing actions where earthquake forces are high
In certain cases in particular for low-rise residential buildings such as single occupancy houses or two-family
houses the roof structures can be made of wooden beams and can be deformable even in new buildings In
these cases or in the upper storeys of multi-storey multiple-occupancy residential buildings wall designs
can be governed by resistance to out-of-plane forces
22 SERVICE COMMERCIAL AND INDUSTRIAL BUILDINGS
In service commercial and industrial buildings where masonry walls also reinforced are used as infill walls
with non-structural function their structural design is usually governed only by the resistance to wind and
earthquake forces as the gravity loads are assumed to be carried by the resisting frames In these buildings
the walls must have sufficient in-plane flexural resistance to span between frame members and other
supports Deflection compatibility between frames and walls has to be taken into account in particular if
these buildings are multi-storey buildings In this case the infill walls have to be verified against out-of-plane
earthquake and wind loading to avoid dangerous felt of material that would not compromise the stability of
the building but would prejudice the safety of people
A particular type of building is constituted by the low-rise commercial and industrial buildings generally one-
storey high made with load bearing reinforced masonry instead of infill walls In this case compared to
residential buildings with the same number of storeys the inter-storey height will be generally quite high
(between 5divide8 m) as the inner space has to be used for production or for activities such as sport activities
etc This solution can be chosen for example as it allows obtaining good indoor environmental conditions
suitable for food processing (Figure 5) or for recreational activities (Figure 6)
In this case it is possible to find both deformable (Figure 7) and stiff (Figure 8) roof structures according to
the construction system chosen by the designer The presence of one or the other will influence the
behaviour of the walls If the roof is stiff the horizontal action is mainly distributed to the in-plane loaded
walls The out-of-plane walls in case of seismic action are mainly loaded by the action coming from their
own mass where the roof can be considered a very stiff elastic restraint and act only for its dead-load If the
building is made with deformable roof this is not able to distribute the horizontal load to the in-plane walls In
this case the out-of-plane forces will be dominant In case of seismic action the walls can be tentatively
considered as cantilevers with a vertical load applied at the top and a horizontal load due to the masses of
both the roof and the wall itself The two resulting static schemes of the reinforced masonry walls are
represented in Figure 9
Design of masonry walls D62 Page 8 of 106
Figure 5 Parmigiano Reggiano factory in Ramiseto (RE Italy) Figure 6 Sport centre in Reggio Emilia (Italy)
Gluelam beams and metallic cover
Precast RC double T-beams
Precast RC shed
Figure 7 Sketch of the three deformable roof typologies
RC slabs with lightening clay units
Composite steel-concrete slabs
Steel beams and collaborating RC slab
Figure 8 Sketch of the three rigid roof typologies
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 3 of 106
53 HOLLOW CLAY UNITS 44 531 Geometry and boundary conditions 44 532 Material properties 45 534 Design for vertical loading 52 534 Design charts 53
54 CONCRETE MASONRY UNITS 54 541 Geometry and boundary conditions 54 542 Material properties 55 543 Design for vertical loading 55 544 Design charts 56
6 DESIGN OF WALLS FOR IN-PLANE LOADING 57 61 INTRODUCTION 57 62 PERFORATED CLAY UNITS 59
621 Geometry and boundary conditions 59 622 Material properties 59 623 In-plane wall design 60 624 Design charts 63
63 HOLLOW CLAY UNITS 68 631 Geometry and boundary conditions 68 632 Material properties 69 633 In-plane wall design 69 634 Design charts 71
64 CONCRETE MASONRY UNITS 78 641 Geometry and boundary conditions 78 642 Material properties 80 643 In-plane wall design 81 644 Design charts 83
7 DESIGN OF WALLS FOR OUT-OF-PLANE LOADING 87 71 INTRODUCTION 87 72 PERFORATED CLAY UNITS 87
721 Geometry and boundary conditions 87 722 Material properties 88 723 Out of plane wall design 88 724 Design charts 91
73 HOLLOW CLAY UNITS 93 731 Geometry and boundary conditions 93 732 Material properties 93 733 Out of plane wall design 94 734 Design charts 95
Design of masonry walls D62 Page 4 of 106
74 CONCRETE MASONRY UNITS 97 741 Geometry and boundary conditions 97 742 Material properties 97 743 Out-of-plane wall design 98 744 Design charts 98
8 OTHER DESIGN ASPECTS 101 81 DURABILITY 101 82 SERVICEABILITY LIMIT STATE 101
REFERENCES 103 ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE 105
Design of masonry walls D62 Page 5 of 106
1 INTRODUCTION
11 DESCRIPTION AND OBJECTIVES OF THE WORK PACKAGE
The major aim of DISWall project is the proposal of innovative systems for reinforced masonry walls The
validation of the feasibility of the systems as a whole to be used as an industrialized solution involves the
study of the technical economical and mechanical performance The WP3 WP4 WP5 are devoted to this
studies by means of design and production of materials development and construction of reinforced
masonry systems and by means of experimental and numerical simulations The workpackage 6 is aimed at
producing guidelines for end users and practitioners regarding the design of masonry walls with vertical and
horizontal reinforcement including design charts and a software code for the design of masonry walls made
with the proposed construction systems These products of the WP6 are of crucial importance to ensure the
commercial expansion and the exploitation of the intended technology as they provide the potential users
(designer architects and engineers and construction companies) with understandable easy to use and
sound design tools These rules and tools should provide the average user with easy criteria to safely design
masonry walls for most of the expected situations Moreover the interaction and the incorporation of these
recommendations into norms and codes (eg EC6 and EC8) can vanish any mistrust and strongly foster the
use of the intended structural solutions For special cases the designer will be addressed to scientific and
technical reports and the use of more complex software The workpackage 6 is mainly based on the
experience of WP5 through which the understanding of the behaviour of reinforced masonry walls under
service and ultimate conditions subjected to diverse possible actions has been gained
12 OBJECTIVES AND STRUCTURE OF THE DELIVERABLE
These guidelines give general recommendations for the structural design of reinforced masonry walls
They cover the main aspects related to how to calculate and design masonry walls built with perforated clay
units hollow clay units and concrete units and also include design charts They are not intended to cover any
other type of reinforced masonry besides those above mentioned and any other aspect of design such as
acoustic thermal etc The aspect related to the construction are covered by D75
The recommendations in these guidelines are based on literature research and code recommendations and
on the experience gained through the testing and modelling of masonry wall specimens in the framework of
the DISWall project They are intended in particular for those end-users (architects engineers construction
companies etc) that are involved with the conception and the design of the buildings
The guidelines are structured into seven main sections After the introduction there is a short reference to
the type of buildings that can be built with the proposed construction systems and a description of the
systems Following some general aspects of the structural design are reported and the aspects of design
for in-plane and out-of-plane loadings are described Other design aspects related to the structural
performance of the buildings are briefly described Finally some reference publications and relevant
standards are listed
Design of masonry walls D62 Page 6 of 106
2 TYPES OF CONSTRUCTION
Some typical example of buildings that can be built with the proposed reinforced masonry systems is given in
the deliverable D75 section 8 In the following the different building typologies are divided according to the
typical structural behaviour that can be recognized for each of them
21 RESIDENTIAL BUILDINGS
The common form of residential construction in Europe varies from the single occupancy house (Figure 1)
one or two-storey high to the multiple-occupancy residential buildings of load bearing masonry which are
commonly constituted by two or three-storey when they are built of unreinforced masonry but can reach
relevant height (five-storey or more) when they are built with reinforced masonry (Figure 2) Intermediate
types of buildings include two-storey semi-detached two-family houses (Figure 3) or attached row houses
(Figure 4) In these buildings the masonry walls carry the gravity loads and they usually support concrete
floor slabs and roofs which are characterized by adequate in-plane stiffness The inter-storey height is
generally low around 270 m
Figure 1 One-family house in San Gregorio
nelle Alpi (BL Italy) Figure 2 Residential complex in Colle Aperto
(MN Italy)
Figure 3 Two-family house in Peron di Sedico
(BL Italy) Figure 4 Eight row houses in Alberi di Vigatto
(PR Italy)
In these structures the masonry walls must provide the resistance to horizontal in-plane (shear) forces with
the floor and roof acting as diaphragms to distribute forces to the walls Very often the lateral (out-of-plane)
Design of masonry walls D62 Page 7 of 106
forces from wind are taken into account in the design by calculating the correspondent eccentricity in the
vertical forces and by reducing accordingly the compression strength of masonry in the vertical load
verifications or can be carryed out directly out-of-plane bending moment verification in the case of
reinforced masonry In case of stiff floors and roofs the out-of-plane verifications for the load bearing walls is
generally carried out separately in the hypothesis of double hinges at the wall bottom and top by comparing
the resisting out-of-plane bending moment with the design bending moment However the in-plane shear
forces are generally the governing actions where earthquake forces are high
In certain cases in particular for low-rise residential buildings such as single occupancy houses or two-family
houses the roof structures can be made of wooden beams and can be deformable even in new buildings In
these cases or in the upper storeys of multi-storey multiple-occupancy residential buildings wall designs
can be governed by resistance to out-of-plane forces
22 SERVICE COMMERCIAL AND INDUSTRIAL BUILDINGS
In service commercial and industrial buildings where masonry walls also reinforced are used as infill walls
with non-structural function their structural design is usually governed only by the resistance to wind and
earthquake forces as the gravity loads are assumed to be carried by the resisting frames In these buildings
the walls must have sufficient in-plane flexural resistance to span between frame members and other
supports Deflection compatibility between frames and walls has to be taken into account in particular if
these buildings are multi-storey buildings In this case the infill walls have to be verified against out-of-plane
earthquake and wind loading to avoid dangerous felt of material that would not compromise the stability of
the building but would prejudice the safety of people
A particular type of building is constituted by the low-rise commercial and industrial buildings generally one-
storey high made with load bearing reinforced masonry instead of infill walls In this case compared to
residential buildings with the same number of storeys the inter-storey height will be generally quite high
(between 5divide8 m) as the inner space has to be used for production or for activities such as sport activities
etc This solution can be chosen for example as it allows obtaining good indoor environmental conditions
suitable for food processing (Figure 5) or for recreational activities (Figure 6)
In this case it is possible to find both deformable (Figure 7) and stiff (Figure 8) roof structures according to
the construction system chosen by the designer The presence of one or the other will influence the
behaviour of the walls If the roof is stiff the horizontal action is mainly distributed to the in-plane loaded
walls The out-of-plane walls in case of seismic action are mainly loaded by the action coming from their
own mass where the roof can be considered a very stiff elastic restraint and act only for its dead-load If the
building is made with deformable roof this is not able to distribute the horizontal load to the in-plane walls In
this case the out-of-plane forces will be dominant In case of seismic action the walls can be tentatively
considered as cantilevers with a vertical load applied at the top and a horizontal load due to the masses of
both the roof and the wall itself The two resulting static schemes of the reinforced masonry walls are
represented in Figure 9
Design of masonry walls D62 Page 8 of 106
Figure 5 Parmigiano Reggiano factory in Ramiseto (RE Italy) Figure 6 Sport centre in Reggio Emilia (Italy)
Gluelam beams and metallic cover
Precast RC double T-beams
Precast RC shed
Figure 7 Sketch of the three deformable roof typologies
RC slabs with lightening clay units
Composite steel-concrete slabs
Steel beams and collaborating RC slab
Figure 8 Sketch of the three rigid roof typologies
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 4 of 106
74 CONCRETE MASONRY UNITS 97 741 Geometry and boundary conditions 97 742 Material properties 97 743 Out-of-plane wall design 98 744 Design charts 98
8 OTHER DESIGN ASPECTS 101 81 DURABILITY 101 82 SERVICEABILITY LIMIT STATE 101
REFERENCES 103 ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE 105
Design of masonry walls D62 Page 5 of 106
1 INTRODUCTION
11 DESCRIPTION AND OBJECTIVES OF THE WORK PACKAGE
The major aim of DISWall project is the proposal of innovative systems for reinforced masonry walls The
validation of the feasibility of the systems as a whole to be used as an industrialized solution involves the
study of the technical economical and mechanical performance The WP3 WP4 WP5 are devoted to this
studies by means of design and production of materials development and construction of reinforced
masonry systems and by means of experimental and numerical simulations The workpackage 6 is aimed at
producing guidelines for end users and practitioners regarding the design of masonry walls with vertical and
horizontal reinforcement including design charts and a software code for the design of masonry walls made
with the proposed construction systems These products of the WP6 are of crucial importance to ensure the
commercial expansion and the exploitation of the intended technology as they provide the potential users
(designer architects and engineers and construction companies) with understandable easy to use and
sound design tools These rules and tools should provide the average user with easy criteria to safely design
masonry walls for most of the expected situations Moreover the interaction and the incorporation of these
recommendations into norms and codes (eg EC6 and EC8) can vanish any mistrust and strongly foster the
use of the intended structural solutions For special cases the designer will be addressed to scientific and
technical reports and the use of more complex software The workpackage 6 is mainly based on the
experience of WP5 through which the understanding of the behaviour of reinforced masonry walls under
service and ultimate conditions subjected to diverse possible actions has been gained
12 OBJECTIVES AND STRUCTURE OF THE DELIVERABLE
These guidelines give general recommendations for the structural design of reinforced masonry walls
They cover the main aspects related to how to calculate and design masonry walls built with perforated clay
units hollow clay units and concrete units and also include design charts They are not intended to cover any
other type of reinforced masonry besides those above mentioned and any other aspect of design such as
acoustic thermal etc The aspect related to the construction are covered by D75
The recommendations in these guidelines are based on literature research and code recommendations and
on the experience gained through the testing and modelling of masonry wall specimens in the framework of
the DISWall project They are intended in particular for those end-users (architects engineers construction
companies etc) that are involved with the conception and the design of the buildings
The guidelines are structured into seven main sections After the introduction there is a short reference to
the type of buildings that can be built with the proposed construction systems and a description of the
systems Following some general aspects of the structural design are reported and the aspects of design
for in-plane and out-of-plane loadings are described Other design aspects related to the structural
performance of the buildings are briefly described Finally some reference publications and relevant
standards are listed
Design of masonry walls D62 Page 6 of 106
2 TYPES OF CONSTRUCTION
Some typical example of buildings that can be built with the proposed reinforced masonry systems is given in
the deliverable D75 section 8 In the following the different building typologies are divided according to the
typical structural behaviour that can be recognized for each of them
21 RESIDENTIAL BUILDINGS
The common form of residential construction in Europe varies from the single occupancy house (Figure 1)
one or two-storey high to the multiple-occupancy residential buildings of load bearing masonry which are
commonly constituted by two or three-storey when they are built of unreinforced masonry but can reach
relevant height (five-storey or more) when they are built with reinforced masonry (Figure 2) Intermediate
types of buildings include two-storey semi-detached two-family houses (Figure 3) or attached row houses
(Figure 4) In these buildings the masonry walls carry the gravity loads and they usually support concrete
floor slabs and roofs which are characterized by adequate in-plane stiffness The inter-storey height is
generally low around 270 m
Figure 1 One-family house in San Gregorio
nelle Alpi (BL Italy) Figure 2 Residential complex in Colle Aperto
(MN Italy)
Figure 3 Two-family house in Peron di Sedico
(BL Italy) Figure 4 Eight row houses in Alberi di Vigatto
(PR Italy)
In these structures the masonry walls must provide the resistance to horizontal in-plane (shear) forces with
the floor and roof acting as diaphragms to distribute forces to the walls Very often the lateral (out-of-plane)
Design of masonry walls D62 Page 7 of 106
forces from wind are taken into account in the design by calculating the correspondent eccentricity in the
vertical forces and by reducing accordingly the compression strength of masonry in the vertical load
verifications or can be carryed out directly out-of-plane bending moment verification in the case of
reinforced masonry In case of stiff floors and roofs the out-of-plane verifications for the load bearing walls is
generally carried out separately in the hypothesis of double hinges at the wall bottom and top by comparing
the resisting out-of-plane bending moment with the design bending moment However the in-plane shear
forces are generally the governing actions where earthquake forces are high
In certain cases in particular for low-rise residential buildings such as single occupancy houses or two-family
houses the roof structures can be made of wooden beams and can be deformable even in new buildings In
these cases or in the upper storeys of multi-storey multiple-occupancy residential buildings wall designs
can be governed by resistance to out-of-plane forces
22 SERVICE COMMERCIAL AND INDUSTRIAL BUILDINGS
In service commercial and industrial buildings where masonry walls also reinforced are used as infill walls
with non-structural function their structural design is usually governed only by the resistance to wind and
earthquake forces as the gravity loads are assumed to be carried by the resisting frames In these buildings
the walls must have sufficient in-plane flexural resistance to span between frame members and other
supports Deflection compatibility between frames and walls has to be taken into account in particular if
these buildings are multi-storey buildings In this case the infill walls have to be verified against out-of-plane
earthquake and wind loading to avoid dangerous felt of material that would not compromise the stability of
the building but would prejudice the safety of people
A particular type of building is constituted by the low-rise commercial and industrial buildings generally one-
storey high made with load bearing reinforced masonry instead of infill walls In this case compared to
residential buildings with the same number of storeys the inter-storey height will be generally quite high
(between 5divide8 m) as the inner space has to be used for production or for activities such as sport activities
etc This solution can be chosen for example as it allows obtaining good indoor environmental conditions
suitable for food processing (Figure 5) or for recreational activities (Figure 6)
In this case it is possible to find both deformable (Figure 7) and stiff (Figure 8) roof structures according to
the construction system chosen by the designer The presence of one or the other will influence the
behaviour of the walls If the roof is stiff the horizontal action is mainly distributed to the in-plane loaded
walls The out-of-plane walls in case of seismic action are mainly loaded by the action coming from their
own mass where the roof can be considered a very stiff elastic restraint and act only for its dead-load If the
building is made with deformable roof this is not able to distribute the horizontal load to the in-plane walls In
this case the out-of-plane forces will be dominant In case of seismic action the walls can be tentatively
considered as cantilevers with a vertical load applied at the top and a horizontal load due to the masses of
both the roof and the wall itself The two resulting static schemes of the reinforced masonry walls are
represented in Figure 9
Design of masonry walls D62 Page 8 of 106
Figure 5 Parmigiano Reggiano factory in Ramiseto (RE Italy) Figure 6 Sport centre in Reggio Emilia (Italy)
Gluelam beams and metallic cover
Precast RC double T-beams
Precast RC shed
Figure 7 Sketch of the three deformable roof typologies
RC slabs with lightening clay units
Composite steel-concrete slabs
Steel beams and collaborating RC slab
Figure 8 Sketch of the three rigid roof typologies
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 5 of 106
1 INTRODUCTION
11 DESCRIPTION AND OBJECTIVES OF THE WORK PACKAGE
The major aim of DISWall project is the proposal of innovative systems for reinforced masonry walls The
validation of the feasibility of the systems as a whole to be used as an industrialized solution involves the
study of the technical economical and mechanical performance The WP3 WP4 WP5 are devoted to this
studies by means of design and production of materials development and construction of reinforced
masonry systems and by means of experimental and numerical simulations The workpackage 6 is aimed at
producing guidelines for end users and practitioners regarding the design of masonry walls with vertical and
horizontal reinforcement including design charts and a software code for the design of masonry walls made
with the proposed construction systems These products of the WP6 are of crucial importance to ensure the
commercial expansion and the exploitation of the intended technology as they provide the potential users
(designer architects and engineers and construction companies) with understandable easy to use and
sound design tools These rules and tools should provide the average user with easy criteria to safely design
masonry walls for most of the expected situations Moreover the interaction and the incorporation of these
recommendations into norms and codes (eg EC6 and EC8) can vanish any mistrust and strongly foster the
use of the intended structural solutions For special cases the designer will be addressed to scientific and
technical reports and the use of more complex software The workpackage 6 is mainly based on the
experience of WP5 through which the understanding of the behaviour of reinforced masonry walls under
service and ultimate conditions subjected to diverse possible actions has been gained
12 OBJECTIVES AND STRUCTURE OF THE DELIVERABLE
These guidelines give general recommendations for the structural design of reinforced masonry walls
They cover the main aspects related to how to calculate and design masonry walls built with perforated clay
units hollow clay units and concrete units and also include design charts They are not intended to cover any
other type of reinforced masonry besides those above mentioned and any other aspect of design such as
acoustic thermal etc The aspect related to the construction are covered by D75
The recommendations in these guidelines are based on literature research and code recommendations and
on the experience gained through the testing and modelling of masonry wall specimens in the framework of
the DISWall project They are intended in particular for those end-users (architects engineers construction
companies etc) that are involved with the conception and the design of the buildings
The guidelines are structured into seven main sections After the introduction there is a short reference to
the type of buildings that can be built with the proposed construction systems and a description of the
systems Following some general aspects of the structural design are reported and the aspects of design
for in-plane and out-of-plane loadings are described Other design aspects related to the structural
performance of the buildings are briefly described Finally some reference publications and relevant
standards are listed
Design of masonry walls D62 Page 6 of 106
2 TYPES OF CONSTRUCTION
Some typical example of buildings that can be built with the proposed reinforced masonry systems is given in
the deliverable D75 section 8 In the following the different building typologies are divided according to the
typical structural behaviour that can be recognized for each of them
21 RESIDENTIAL BUILDINGS
The common form of residential construction in Europe varies from the single occupancy house (Figure 1)
one or two-storey high to the multiple-occupancy residential buildings of load bearing masonry which are
commonly constituted by two or three-storey when they are built of unreinforced masonry but can reach
relevant height (five-storey or more) when they are built with reinforced masonry (Figure 2) Intermediate
types of buildings include two-storey semi-detached two-family houses (Figure 3) or attached row houses
(Figure 4) In these buildings the masonry walls carry the gravity loads and they usually support concrete
floor slabs and roofs which are characterized by adequate in-plane stiffness The inter-storey height is
generally low around 270 m
Figure 1 One-family house in San Gregorio
nelle Alpi (BL Italy) Figure 2 Residential complex in Colle Aperto
(MN Italy)
Figure 3 Two-family house in Peron di Sedico
(BL Italy) Figure 4 Eight row houses in Alberi di Vigatto
(PR Italy)
In these structures the masonry walls must provide the resistance to horizontal in-plane (shear) forces with
the floor and roof acting as diaphragms to distribute forces to the walls Very often the lateral (out-of-plane)
Design of masonry walls D62 Page 7 of 106
forces from wind are taken into account in the design by calculating the correspondent eccentricity in the
vertical forces and by reducing accordingly the compression strength of masonry in the vertical load
verifications or can be carryed out directly out-of-plane bending moment verification in the case of
reinforced masonry In case of stiff floors and roofs the out-of-plane verifications for the load bearing walls is
generally carried out separately in the hypothesis of double hinges at the wall bottom and top by comparing
the resisting out-of-plane bending moment with the design bending moment However the in-plane shear
forces are generally the governing actions where earthquake forces are high
In certain cases in particular for low-rise residential buildings such as single occupancy houses or two-family
houses the roof structures can be made of wooden beams and can be deformable even in new buildings In
these cases or in the upper storeys of multi-storey multiple-occupancy residential buildings wall designs
can be governed by resistance to out-of-plane forces
22 SERVICE COMMERCIAL AND INDUSTRIAL BUILDINGS
In service commercial and industrial buildings where masonry walls also reinforced are used as infill walls
with non-structural function their structural design is usually governed only by the resistance to wind and
earthquake forces as the gravity loads are assumed to be carried by the resisting frames In these buildings
the walls must have sufficient in-plane flexural resistance to span between frame members and other
supports Deflection compatibility between frames and walls has to be taken into account in particular if
these buildings are multi-storey buildings In this case the infill walls have to be verified against out-of-plane
earthquake and wind loading to avoid dangerous felt of material that would not compromise the stability of
the building but would prejudice the safety of people
A particular type of building is constituted by the low-rise commercial and industrial buildings generally one-
storey high made with load bearing reinforced masonry instead of infill walls In this case compared to
residential buildings with the same number of storeys the inter-storey height will be generally quite high
(between 5divide8 m) as the inner space has to be used for production or for activities such as sport activities
etc This solution can be chosen for example as it allows obtaining good indoor environmental conditions
suitable for food processing (Figure 5) or for recreational activities (Figure 6)
In this case it is possible to find both deformable (Figure 7) and stiff (Figure 8) roof structures according to
the construction system chosen by the designer The presence of one or the other will influence the
behaviour of the walls If the roof is stiff the horizontal action is mainly distributed to the in-plane loaded
walls The out-of-plane walls in case of seismic action are mainly loaded by the action coming from their
own mass where the roof can be considered a very stiff elastic restraint and act only for its dead-load If the
building is made with deformable roof this is not able to distribute the horizontal load to the in-plane walls In
this case the out-of-plane forces will be dominant In case of seismic action the walls can be tentatively
considered as cantilevers with a vertical load applied at the top and a horizontal load due to the masses of
both the roof and the wall itself The two resulting static schemes of the reinforced masonry walls are
represented in Figure 9
Design of masonry walls D62 Page 8 of 106
Figure 5 Parmigiano Reggiano factory in Ramiseto (RE Italy) Figure 6 Sport centre in Reggio Emilia (Italy)
Gluelam beams and metallic cover
Precast RC double T-beams
Precast RC shed
Figure 7 Sketch of the three deformable roof typologies
RC slabs with lightening clay units
Composite steel-concrete slabs
Steel beams and collaborating RC slab
Figure 8 Sketch of the three rigid roof typologies
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 6 of 106
2 TYPES OF CONSTRUCTION
Some typical example of buildings that can be built with the proposed reinforced masonry systems is given in
the deliverable D75 section 8 In the following the different building typologies are divided according to the
typical structural behaviour that can be recognized for each of them
21 RESIDENTIAL BUILDINGS
The common form of residential construction in Europe varies from the single occupancy house (Figure 1)
one or two-storey high to the multiple-occupancy residential buildings of load bearing masonry which are
commonly constituted by two or three-storey when they are built of unreinforced masonry but can reach
relevant height (five-storey or more) when they are built with reinforced masonry (Figure 2) Intermediate
types of buildings include two-storey semi-detached two-family houses (Figure 3) or attached row houses
(Figure 4) In these buildings the masonry walls carry the gravity loads and they usually support concrete
floor slabs and roofs which are characterized by adequate in-plane stiffness The inter-storey height is
generally low around 270 m
Figure 1 One-family house in San Gregorio
nelle Alpi (BL Italy) Figure 2 Residential complex in Colle Aperto
(MN Italy)
Figure 3 Two-family house in Peron di Sedico
(BL Italy) Figure 4 Eight row houses in Alberi di Vigatto
(PR Italy)
In these structures the masonry walls must provide the resistance to horizontal in-plane (shear) forces with
the floor and roof acting as diaphragms to distribute forces to the walls Very often the lateral (out-of-plane)
Design of masonry walls D62 Page 7 of 106
forces from wind are taken into account in the design by calculating the correspondent eccentricity in the
vertical forces and by reducing accordingly the compression strength of masonry in the vertical load
verifications or can be carryed out directly out-of-plane bending moment verification in the case of
reinforced masonry In case of stiff floors and roofs the out-of-plane verifications for the load bearing walls is
generally carried out separately in the hypothesis of double hinges at the wall bottom and top by comparing
the resisting out-of-plane bending moment with the design bending moment However the in-plane shear
forces are generally the governing actions where earthquake forces are high
In certain cases in particular for low-rise residential buildings such as single occupancy houses or two-family
houses the roof structures can be made of wooden beams and can be deformable even in new buildings In
these cases or in the upper storeys of multi-storey multiple-occupancy residential buildings wall designs
can be governed by resistance to out-of-plane forces
22 SERVICE COMMERCIAL AND INDUSTRIAL BUILDINGS
In service commercial and industrial buildings where masonry walls also reinforced are used as infill walls
with non-structural function their structural design is usually governed only by the resistance to wind and
earthquake forces as the gravity loads are assumed to be carried by the resisting frames In these buildings
the walls must have sufficient in-plane flexural resistance to span between frame members and other
supports Deflection compatibility between frames and walls has to be taken into account in particular if
these buildings are multi-storey buildings In this case the infill walls have to be verified against out-of-plane
earthquake and wind loading to avoid dangerous felt of material that would not compromise the stability of
the building but would prejudice the safety of people
A particular type of building is constituted by the low-rise commercial and industrial buildings generally one-
storey high made with load bearing reinforced masonry instead of infill walls In this case compared to
residential buildings with the same number of storeys the inter-storey height will be generally quite high
(between 5divide8 m) as the inner space has to be used for production or for activities such as sport activities
etc This solution can be chosen for example as it allows obtaining good indoor environmental conditions
suitable for food processing (Figure 5) or for recreational activities (Figure 6)
In this case it is possible to find both deformable (Figure 7) and stiff (Figure 8) roof structures according to
the construction system chosen by the designer The presence of one or the other will influence the
behaviour of the walls If the roof is stiff the horizontal action is mainly distributed to the in-plane loaded
walls The out-of-plane walls in case of seismic action are mainly loaded by the action coming from their
own mass where the roof can be considered a very stiff elastic restraint and act only for its dead-load If the
building is made with deformable roof this is not able to distribute the horizontal load to the in-plane walls In
this case the out-of-plane forces will be dominant In case of seismic action the walls can be tentatively
considered as cantilevers with a vertical load applied at the top and a horizontal load due to the masses of
both the roof and the wall itself The two resulting static schemes of the reinforced masonry walls are
represented in Figure 9
Design of masonry walls D62 Page 8 of 106
Figure 5 Parmigiano Reggiano factory in Ramiseto (RE Italy) Figure 6 Sport centre in Reggio Emilia (Italy)
Gluelam beams and metallic cover
Precast RC double T-beams
Precast RC shed
Figure 7 Sketch of the three deformable roof typologies
RC slabs with lightening clay units
Composite steel-concrete slabs
Steel beams and collaborating RC slab
Figure 8 Sketch of the three rigid roof typologies
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 7 of 106
forces from wind are taken into account in the design by calculating the correspondent eccentricity in the
vertical forces and by reducing accordingly the compression strength of masonry in the vertical load
verifications or can be carryed out directly out-of-plane bending moment verification in the case of
reinforced masonry In case of stiff floors and roofs the out-of-plane verifications for the load bearing walls is
generally carried out separately in the hypothesis of double hinges at the wall bottom and top by comparing
the resisting out-of-plane bending moment with the design bending moment However the in-plane shear
forces are generally the governing actions where earthquake forces are high
In certain cases in particular for low-rise residential buildings such as single occupancy houses or two-family
houses the roof structures can be made of wooden beams and can be deformable even in new buildings In
these cases or in the upper storeys of multi-storey multiple-occupancy residential buildings wall designs
can be governed by resistance to out-of-plane forces
22 SERVICE COMMERCIAL AND INDUSTRIAL BUILDINGS
In service commercial and industrial buildings where masonry walls also reinforced are used as infill walls
with non-structural function their structural design is usually governed only by the resistance to wind and
earthquake forces as the gravity loads are assumed to be carried by the resisting frames In these buildings
the walls must have sufficient in-plane flexural resistance to span between frame members and other
supports Deflection compatibility between frames and walls has to be taken into account in particular if
these buildings are multi-storey buildings In this case the infill walls have to be verified against out-of-plane
earthquake and wind loading to avoid dangerous felt of material that would not compromise the stability of
the building but would prejudice the safety of people
A particular type of building is constituted by the low-rise commercial and industrial buildings generally one-
storey high made with load bearing reinforced masonry instead of infill walls In this case compared to
residential buildings with the same number of storeys the inter-storey height will be generally quite high
(between 5divide8 m) as the inner space has to be used for production or for activities such as sport activities
etc This solution can be chosen for example as it allows obtaining good indoor environmental conditions
suitable for food processing (Figure 5) or for recreational activities (Figure 6)
In this case it is possible to find both deformable (Figure 7) and stiff (Figure 8) roof structures according to
the construction system chosen by the designer The presence of one or the other will influence the
behaviour of the walls If the roof is stiff the horizontal action is mainly distributed to the in-plane loaded
walls The out-of-plane walls in case of seismic action are mainly loaded by the action coming from their
own mass where the roof can be considered a very stiff elastic restraint and act only for its dead-load If the
building is made with deformable roof this is not able to distribute the horizontal load to the in-plane walls In
this case the out-of-plane forces will be dominant In case of seismic action the walls can be tentatively
considered as cantilevers with a vertical load applied at the top and a horizontal load due to the masses of
both the roof and the wall itself The two resulting static schemes of the reinforced masonry walls are
represented in Figure 9
Design of masonry walls D62 Page 8 of 106
Figure 5 Parmigiano Reggiano factory in Ramiseto (RE Italy) Figure 6 Sport centre in Reggio Emilia (Italy)
Gluelam beams and metallic cover
Precast RC double T-beams
Precast RC shed
Figure 7 Sketch of the three deformable roof typologies
RC slabs with lightening clay units
Composite steel-concrete slabs
Steel beams and collaborating RC slab
Figure 8 Sketch of the three rigid roof typologies
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 8 of 106
Figure 5 Parmigiano Reggiano factory in Ramiseto (RE Italy) Figure 6 Sport centre in Reggio Emilia (Italy)
Gluelam beams and metallic cover
Precast RC double T-beams
Precast RC shed
Figure 7 Sketch of the three deformable roof typologies
RC slabs with lightening clay units
Composite steel-concrete slabs
Steel beams and collaborating RC slab
Figure 8 Sketch of the three rigid roof typologies
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 9 of 106
Figure 9 Static schemes for out-of-plane walls with deformable roof (left) with rigid roof (right)
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 10 of 106
3 DESCRIPTION OF THE CONSTRUCTION SYSTEMS
31 PERFORATED CLAY UNITS
Italy as many other countries facing the Mediterranean basin (Portugal Slovenia Greece etc) is almost
entirely affected by a low to high seismic hazard Load bearing masonry buildings where walls are made of
perforated clay units are largely used for the construction of residential buildings as well as larger buildings
with industrial or services destination Within this project one of the studied construction system is aimed at
improving the behaviour of walls under in-plane actions for medium to low size residential buildings
characterized by low rise walls (about 27m) see sect 311 The second construction system is aimed at
improving the out-of-plane resistance of reinforced masonry walls in the case of slender tall walls (6divide8 m
high) to be used for the construction of large buildings such as gymnasiums industrial buildings etc (see sect
312)
311 Perforated clay units for in-plane masonry walls
This reinforced masonry construction system with concentrated vertical reinforcement and similar to
confined masonry is made by using a special clay unit with horizontal holes and recesses for the
accommodation of the horizontal reinforcement and an ordinary clay unit with vertical holes for the confining
columns that contain the vertical reinforcement (Figure 10 Figure 11)
Figure 10 Construction system with horizontally
perforated clay units Front view and cross sections
Figure 11 Construction system with horizontally perforated clay units Axonometric view of the corner
detail
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 11 of 106
The wall width in the figures is 300 mm but the width can be increased in a modular way Two types of
horizontal reinforcement can be used ordinary ribbed steel rebars or prefabricated steel trusses of the
Murfor type The mortar to be used with this reinforced masonry system is a premixed M10 cement mortar
with 0divide4 mm aggregate size and additives to improve plasticity and adhesion properties The mortar is
developed to be suitable for both the filling of the vertical cavities and the bedding of the horizontal joints
Figure 10 and Figure 11 show the developed masonry system
The system which makes use of horizontally perforated clay units that is a very traditional construction
technique for all the countries facing the Mediterranean basin has been developed mainly to be used in
small residential buildings that are generally built with stiff floors and roofs and in which the walls have to
withstand in-plane actions This masonry system has been developed in order to optimize the bond of the
horizontal reinforcement to improve durability thanks to the adequate covering provided all around of the
reinforcement and to make easier and more precise the placement of the horizontal reinforcement It is also
possible that the units with horizontally oriented webs can obtain a better shear stress transfer to the
vertical confining columns
312 Perforated clay units for out-of-plane masonry walls
This construction system is made by using vertically perforated clay units and is developed and aimed at
building mainly tall load bearing reinforced masonry walls for factories sport centres etc These types of
structures have to resist out-of-plane actions in particular when they are in the presence of deformable
roofs This system is based on the use of traditional lsquoHrsquo shaped units which are threaded over the top of the
bar and requires one or several bar overlapping along the wall height or of lsquoCrsquo shaped units which can be
easily put in place after the vertical reinforcement has been already placed Figure 12 shows the developed
masonry system
Figure 12 Construction system with vertically perforated clay units Front view and cross sections
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be
TASSIOS TP (1998) ldquoMeccanica delle muraturardquo Liguori Editore Napoli (in italian)
TOMAZEVIC M (1999) Earthquake-Resistant design of masonry buildings ndash vol I Series on Innovation in
structures and Construction Elnashai A S amp Dowling P J
Design of masonry walls D62 Page 105 of 106
ANNEX EXPLANATORY NOTES FOR THE USE OF THE SOFTWARE
As part of the project deliverable D63 it was foreseen to produce the So-Wall software for the reinforced
masonry walls verification Information on how to use the software are given in this annex as the software is
based on the design rules reported in section from sect 5 to sect 7 The software allows calculating the resisting
parameters of reinforced masonry walls made with the different construction technologies developed and
tested in the framework of the DISWall project ie reinforced masonry with perforated clay units for resisting
mainly in-plane (ALAN system) and out-of-plane (CISEDIL system) load with hollow clay units (UNIPOR)
with concrete units (CampA) The designer on the basis of the analyses carried out and the knowledge of the
design values of the applied axial load shear and bending moment can carry out the masonry wall
verifications using the So-Wall
The Software code is running within the MS-Excel programme using Visual Basic Scripts Therefore for the
use of the software the execution of macros has to be enabled At the beginning the type of dominant
loading has to be chosen
bull in-plane loadings
or
bull out-of-plane loadings
As suitable design approaches for the general interaction of the two types of loadings does not exist the
user has to make further investigation when relevant interaction is assumed The software carries out the
design process in the Ultimate-Limit-State (ULS) according to the rules presented in this report (D62) If the
Serviceability Limit State (SLS) is not covered by the ULS additional investigation have to be performed by
the user The durability has to be ensured by further checks acc EN 1996-1-1 2005 eg climate conditions
or coating of the reinforcement according to what is reported in section sect 8
For the out-of-plane loadings the relevant design action is the bending in vertical direction For the in-plane
loadings the relevant action is the combined N-M-V loading As reinforced masonry is generally not intended
for axial tension forces this type of loading is not covered by this design software
When the type of loading for which carrying out the verification is inserted the type of masonry has to be
selected By doing this the software automatically switch the calculation of correct formulations according to
what is written in section from sect5 to sect7
Then according to the type of loading the length l and the thickness t of the wall has to be entered (in-plane
loading) or the width b the thickness h and the position of the reinforcement d (out-of-plane loading) have to
be entered (see Figure 99) Some minimum limitations on the geometry are already given by the software
and they reflect the configuration of the developed construction systems The amount of the horizontal and
vertical reinforcement has also to be entered If no horizontal reinforcement is applied the corresponding
value has to be set to zero The effect of opening on the behaviour of reinforced masonry structural elements
has to be considered by dividing the whole wall in several sub-elements
Design of masonry walls D62 Page 106 of 106
Figure 99 Cross section for out-of-plane and in-plane loadings
A list of value of mechanical parameters has to be inserted next These values regard the unit mortar
concrete and reinforcement mechanical properties The symbols used in this section are self-explanatory
and in any case each parameter found into the software is explained in detail into the present deliverable
D62 The compression strength of masonry is calculated according EN 1996-1-1 2005 (pressing the
Calculate f_k button) or entered directly by the user as input parameter For the compression strength of
ALAN masonry the factored compressive strength is directly evaluated by the software given the material
properties and the wall length For the UNIPOR system the approaches from EN 1992 are taken into account
including long term effect of the concrete
The choice of the partial safety factors are made by the user After entering the design loadings the
calculation is started pressing the Design-button The result is given within few seconds The result can also
be checked in the V-N-M-chart Here in the Nd-Md-range the allowable shear loadings VRd are plotted with
different symbols and colours The design action is marked directly within the chart In the main page a
message indicates whereas the masonry section is verified or if not an error message stating which
parameter is outside the safety range is given
For the developers an Admin-Button is available By pressing it all the cells of the worksheet are visible and
can be modified In the end-user version this button and also all worksheets except for the Design- and V-N-
M-Chart-sheets that give the resisting domain of the masonry walls are hidden and protected by a
password
Design of masonry walls D62 Page 12 of 106
The developed lsquoCrsquo shaped unit has also the main objective to allow the uncoupling of the vertical rebars far
from the axis of the wall The un-coupling of the vertical reinforcement guarantees a better out-of-plane
behaviour assuring at the same time an appropriate confining effect on the small reinforced column The
developed premixed M10 cement mortar with 0divide4 mm aggregate size and additives to improve plasticity and
adhesion properties is suitable for both the filling of the vertical cavities and the bedding of the horizontal
joints For the reinforcement traditional ribbed steel rebars can be used and with the lsquoCrsquo shaped units there
is no need of having overlapping even in tall walls Two and three-dimensional prefabricated steel trusses
can be also used for the horizontal and vertical reinforcement respectively They can have some
advantages compared to the rebars for example the easier and better placing and the direct collaboration of
the different longitudinal wires of the three-dimensional truss that brings to a better mechanical behaviour
32 HOLLOW CLAY UNITS
The hollow clay unit system is based on unreinforced masonry systems used in Germany since several
years mostly for load bearing walls with high demands on sound insulation Within these systems the
concrete infill is not activated for the load bearing function
Nevertheless the increased seismic loadings acc to Eurocode 8 and the corresponding national standard
DIN 4149 (2005) made the use of masonry structural elements with higher (shear-) load bearing capacities
necessary Therefore the development focused on the application of reinforcement to increase the in-plane-
shear and also the in-plane bending resistance Out-of-plane loadings are for the mentioned walls in
common types of construction not relevant as the these types of reinforced masonry are used for internal
walls and the exterior walls are usually build using vertically perforated clay units with a high thermal
insulation
For the load bearing capacity vertical and also horizontal reinforcement is necessary (coupling of the vertical
columns and load distribution) Therefore the bricks were modified amongst others to enable the application
of horizontal reinforcement
The system is built on site using thin layer mortar At the end of each row a modified clay unit is used to
avoid leakage The reinforcement is placed as a prefabricated element into the lower row The overlapping of
the horizontal and also the vertical reinforcement is ensured
Design of masonry walls D62 Page 13 of 106
Figure 13 Construction system with hollow clay units
The amount of reinforcement was fixed for horizontal and vertical direction to 4 d 6mm with a spacing of
25cm ie 425 mmsup2m
Figure 14 Reinforcement for the hollow clay unit system plan view
Figure 15 Reinforcement for the hollow clay unit system vertical section
The fixation and anchorage of the vertical reinforcement into the foundation resp RC storey slabs (base of
the wall) is done by single reinforcement bars with a spacing of 25cm The bars are either integrated into the
RC structural member before or glued in after it At the top of the wall also single reinforcement bars are
fixed into the clay elements before placing the concrete infill into the wall
Design of masonry walls D62 Page 14 of 106
33 CONCRETE MASONRY UNITS
Portugal is a country with very different seismic risk zones with low to high seismicity A construction system
is proposed for reinforced masonry walls to be used in general masonry buildings located in zones with
moderate to high seismic hazards and to carry out mainly in-plane loadings The construction system is
based on concrete masonry units whose geometry and mechanical properties have to be specially designed
to be used for structural purposes Two and three hollow cell concrete masonry units were developed in
order to vertical reinforcements can be properly accommodated For this construction system different
possibilities of placing the vertical reinforcements and distinct masonry bonds can be used see Figure 16
and Figure 17 The concrete block with three hollow cells is especially formulated to accommodate uniformly
spaced vertical reinforcement If the traditional masonry bond is used the vertical reinforcements (Murfor
RND Z) can be introduced both in the internal hollow cell and in the hollow cell formed by the frogged ends
In this case both continuous and overlapped vertical reinforcements are possible In both cases and due to
the type of masonry units the horizontal reinforcements are to be placed in the bed joints An important
aspect of this construction system is the filling of the vertical reinforced joints with a modified general
purpose mortar instead the traditional grout so that suitable bond strength between reinforcements and the
masonry can be reached and thus an effective stress transfer mechanism between both materials can be
obtained
(a)
(b)
Figure 16 Construction system based hollow concrete masonry units CMU2c with (a) continuous vertical
joints (b) vertical reinforcements placed in the hollow cells
Design of masonry walls D62 Page 15 of 106
Figure 17 Detail of the intersection of reinforced masonry walls
Design of masonry walls D62 Page 16 of 106
4 GENERAL DESIGN ASPECTS
41 LOADING CONDITIONS
The size of the structural members are primarily governed by the requirement that these elements must
adequately carry all the gravity loads imposed upon them that are vertical loads related to the weight of the
building components or permanent construction and machinery inside the building and the vertical loads
related to the building occupancy due to the use of the building but not related to wind earthquake or dead
loads [Schneider and Dickey 1980] Wind and earthquake produce horizontal lateral loads on a structure
which generate in-plane shear loads and out-of-plane face loads on individual members While both loading
types generate horizontal forces they are different in nature Wind loads are applied directly to the surface of
building elements whereas earthquake loads arise due to the inertia inherent in the building when the
ground moves Consequently the relative forces induced in various building elements are different under the
two types of loading [Lawrence and Page 1999]
In the following some general rules for the determination of the load intensity for the different loading
conditions and the load combinations for the structural design taken from the Eurocodes are given These
rules apply to all the countries of the European Community even if in each country some specific differences
or different values of the loading parameters and the related partial safety factors can be used Finally some
information of the structural behaviour and the mechanism of load transmission in masonry buildings are
given
411 Vertical loading
In this very general category the main distinction is between dead and live load The first can be described
as those loads that remain essentially constant during the life of a structure such as the weight of the
building components or any permanent or stationary construction such as partition or equipment Therefore
the dead load is the vertical load due to the weight of all permanent structural and non-structural components
of a building such as walls floors roofs and fixed equipment [Schneider and Dickey 1980] Generally
reasonably accurate estimate for preliminary design purpose can be made on the basis of the experience
and of the knowledge of the approximate weights of building materials Table 1and Table 2 give the mean
values of density of construction materials such as concrete mortar and masonry other materials such as
wood metals plastics glass and also possible stored materials can be found from a number of sources
and in particular in EN 1991-1-1
The live loads are also referred to as occupancy loads and are those loads which are directly caused by
people furniture machines or other movable objects They may be considered as short-duration loads
since they act intermittently during the life of a structure The codes specify minimum floor live-load
requirements for various types of occupancies or uses [Schneider and Dickey 1980] The imposed loads
can be modelled by uniformly distributed loads line loads or concentrated loads or combinations of these
loads Table 3 gives the values fixed by the EN 1991-1-1 where the type of occupancy can be inferred by
Design of masonry walls D62 Page 17 of 106
the following Table 8 Snow also represents a type of live load to be distributed on roofs Snow loads can be
evaluated according to EN 1991-1-3 taking into account the characteristic value of snow load on the ground
sk given for each site according to the climatic region and the altitude the shape of the roof and in certain
cases of the building by means of the shape coefficient microi the topography of the building location by means
of the exposure coefficient Ce and the reduction of snow loads on roofs with high thermal transmittance (gt 1
Wm2K) because of melting caused by heat loss by means of the thermal coefficient Ct The resulting snow
load for the persistenttransient design situation is thus given by
s = microi Ce Ct sk (41)
Table 1 Density of constructions materials concrete and mortar [after EN 1991-1-1]
Table 2 Density of constructions materials masonry [after EN 1991-1-1]
Design of masonry walls D62 Page 18 of 106
Table 3 Imposed loads on floors balconies and stairs in buildings [after EN 1991-1-1]
412 Wind loading
According to the EN 1991-1-4 wind actions fluctuate with time and act directly as pressures on the external
surfaces of enclosed structures and also act indirectly on the internal surfaces of enclosed structures or
directly on the internal surface of open structures Pressures act on areas of the surface resulting in forces
normal to the surface of the structure or of individual cladding components Generally the wind action is
represented by a simplified set of pressures or forces whose effects are equivalent to the extreme effects of
the turbulent wind
Wind loads can be evaluated according to EN 1991-1-4 taking into account the mean wind velocity vm
determined from the basic wind velocity vb at 10 m above ground level in open country terrain which
depends on the wind climate given for each geographical area and the height variation of the wind
determined from the terrain roughness (roughness factor cr(z)) and orography (orography factor co(z))
vm = vb cr(z) co(z) (42)
To codify wind-load values that may be readily used in design the kinetic energy of wind motion must be first
converted into a dynamic pressure Once defined the air density ρ (with recommended value of 125 kgm3)
and the basic velocity pressure qp
(43)
the peak velocity pressure qp(z) at height z is equal to
(44)
Design of masonry walls D62 Page 19 of 106
where ce(z) is the exposure factor and is equal to the ratio between the peak velocity pressure at the
corresponding height qp(z) and the basic velocity pressure qp at this point the wind pressure acting on the
external surfaces we and on the internal surfaces wi of buildings can be respectively found as
we = qp (ze) cpe (45a)
wi = qp (zi) cpi (45b)
where ze and zi are the reference heights for the external and the internal pressure and depend on the aspect ratio of
the loaded portion of the building hb and cpe and cpi are the pressure coefficients for the external and the internal
pressure which depend on the size and shape of the loaded area In the definition of the wind load also the size
factor cs which takes into account the reduction effect on the wind action due to the non-simultaneity of occurrence of
the peak wind pressures on the surface and the dynamic factor cd which takes into account the increasing effect from
vibrations due to turbulence in resonance with the structure are used
413 Earthquake loading
Earthquake loading is the force generated by horizontal and vertical ground movements due to earthquake
These movements induce inertial forces in the structure related to the distributions of mass and rigidity and
the overall forces produce bending shear and axial effects in the structural members For simplicity
earthquake loading can be converted to equivalent static forces with appropriate allowance for the dynamic
characteristics of the structure foundation conditions etc [Lawrence and Page 1999]
This operation is carried out by representing the impact of ground motion on vibrating structures by an elastic
response spectrum that is a plot of the peak response (displacement velocity or acceleration) of a series of
SDOF systems of varying natural frequency that are forced into motion by the same base vibration or shock
The resulting plot can then be used to pick off the response of any linear system given its period (the
inverse of the frequency) When the maximum acceleration is obtained from the spectrum the maximum
lateral forces to carry out elastic analysis and the following verifications are obtained The elastic response
spectra given by the codes are obtained from different accelerograms and are differentiated on the bases of
the soil characteristics besides the values of the structural damping To take into account in a simplified way
of the non-linearity of the structure the ordinates of the spectra are reduced by means of the behaviour
factors lsquoqrsquo and the design response spectra are obtained
The process for calculating the seismic action according to the EN 1998-1-1 is the following First the
national territories shall be subdivided into seismic zones depending on the local hazard that is described in
terms of a single parameter ie the value of the reference peak ground acceleration on type A ground agR
The reference peak ground acceleration corresponds to the reference return period TNCR of the seismic
action for the no-collapse requirement (or equivalently the reference probability of exceedance in 50 years
PNCR) chosen by the National Authorities An importance factor γI equal to 10 is assigned to this reference
return period For return periods other than the reference related to the importance classes of the building
the design ground acceleration on type A ground ag is equal to agR times the importance factor γI (ag = γIagR)
Design of masonry walls D62 Page 20 of 106
where γI is equal to 12 for relevant buildings and 14 for strategic buildings Ground types A B C D and E
described by the stratigraphic profiles and parameters given in the EN 1998-1-1 shall be used to account for
the influence of local ground conditions on the seismic action
For the horizontal components of the seismic action the elastic response spectrum Se(T) is defined by the
following expressions
(46a)
(46b)
(46c)
(46d)
where Se(T) is the elastic response spectrum T is the vibration period of a linear SDOF system ag is the
design ground acceleration on type A ground (ag = γIagR) TB is the lower limit of the period of the constant
spectral acceleration branch TC is the upper limit of the period of the constant spectral acceleration branch
TD is the value defining the beginning of the constant displacement response range of the spectrum S is the
soil factor η is the damping correction factor with a reference value of η = 1 for 5 viscous damping and
equal to for different values of viscous damping ξ
In the EN 1998-1-1 there are two types of recommended spectra Type 1 and Type 2 where the second is
adopted if the earthquakes that contribute most to the seismic hazard defined for the site for the purpose of
probabilistic hazard assessment have a surface-wave magnitude Ms le 55 The following Table 4 and Figure
18 give values of the soil parameter and the vibration periods describing the recommended Type 1 elastic
response spectra and the corresponding spectra (for 5 viscous damping)
Table 4 Values of the parameters describing the recommended Type 1 elastic response spectra [after EN
1998-1-1]
Design of masonry walls D62 Page 21 of 106
Figure 18 Recommended Type 1 elastic response spectra for ground types A to E (5 damping) [after EN 1998-1-1]
When needed the elastic displacement response spectrum SDe(T) shall be obtained by direct
transformation of the elastic acceleration response spectrum Se(T) using the following expression normally
for vibration periods not exceeding 40 s
(47)
The code also gives the expressions for the evaluation of the elastic response spectrum Sve(T) for the
vertical component of the seismic action
(48a)
(48b)
(48c)
(48d)
where Table 5 gives the recommended values of parameters describing the vertical elastic response
spectra
Table 5 Values of the parameters describing the vertical elastic response spectra [after EN 1998-1-1]
Design of masonry walls D62 Page 22 of 106
As already explained the capacity of the structural systems to resist seismic actions in the non-linear range
generally permits their design for resistance to seismic forces smaller than those corresponding to a linear
elastic response Therefore design spectra obtained by reducing the elastic response spectra by the lsquoqrsquo
behaviour factor can be used in elastic analysis For the horizontal components of the seismic action the
design spectrum Sd(T) shall be defined by the following expressions
(49a)
(49b)
(49c)
(49d)
where ag S TC and TD are as defined in Table 4 for Type 1 spectra Sd(T) is the design spectrum β is the
lower bound factor for the horizontal design spectrum and its recommended value is 02 For the vertical
component of the seismic action the design spectrum is given by expressions (49a) to (49d) with the
design ground acceleration in the vertical direction avg replacing ag S taken as being equal to 10 and the
other parameters as defined in Table 5 Furthermore for the vertical component of the seismic action a
behaviour factor q up to to 15 should generally be adopted for all materials and structural systems whereas
in the specific case of masonry structures the recommended values of behaviour factor are given in Table 6
Table 6 Types of construction and upper limit of the behaviour factor [after EN 1998-1-1]
414 Ultimate limit states load combinations and partial safety factors
According to EN 1990 the ultimate limit states to be verified are the following
a) EQU Loss of static equilibrium of the structure or any part of it considered as a rigid body
Design of masonry walls D62 Page 23 of 106
b) STR Internal failure or excessive deformation of the structure or structural members where the strength
of construction materials of the structure governs
c) GEO Failure or excessive deformation of the ground where the strengths of soil or rock are significant in
providing resistance
d) FAT Fatigue failure of the structure or structural members
At the ultimate limit states for each critical load case the design values of the effects of actions (Ed) shall be
determined by combining the values of actions that are considered to occur simultaneously Each
combination of actions should include a leading variable action (such as wind for example) or an accidental
action The fundamental combination of actions for persistent or transient design situations and the
combination of actions for accidental design situations are respectively given by
(410a)
(410b)
where γG is the partial safety factor for permanent actions Gkj γQ is the partial factor for the variable actions
Qki and γP is the partial factor for the precompression P and are given in Table 7 Ad is the accidental action
and ψ0i is the combination coefficient given in Table 8
Table 7 Recommended values of γ factors for buildings [after EN 1990]
EQU limit state (set A) STRGEO limit state (set B) STRGEO limit state (set C)
Factor γG γQ γG γQ γG γQ
favourable 090 000 100 000 100 000
unfavourable 110 150 135 150 100 130 where the verification of static equilibrium also involves the resistance of structural members for γG values of 135 and 115 can be adopted
In the seismic design the inertial effects of the design seismic action shall be evaluated by taking into
account the presence of the masses associated with the gravity loads appearing in the following combination
of actions
(411)
where ψEi is the combination coefficient for variable action i and takes into account the likelihood of the
variable loads Qki not being present over the entire structure during the earthquake According to EN 1998-
1-1 the combination coefficients ψEi introduced in eq (411) for the calculation of the effects of the seismic
actions shall be computed from the following expression
ψEi = φ ψ2i (412)
Design of masonry walls D62 Page 24 of 106
where the combination coefficients ψ2i for the quasi-permanent value of variable action qi for the design of
buildings is given in EN 1990 and is reported in Table 8 together with the categories of building use and the
the recommended values for φ are listed in Table 9
Table 8 Recommended values of ψ factors for buildings [after EN 1990]
Table 9 Values of φ for calculating ψEi [after EN 1998-1-1]
The combination of actions for seismic design situations for calculating the design value Ed of the effects of
actions in the seismic design situation according to EN 1990 is given by
(413)
where AEd is the design value of the seismic action
Design of masonry walls D62 Page 25 of 106
415 Loading conditions in different National Codes
In Italy a process of adaptation of the structural codes to the Eurocodes has recently started in the field of
seismic design with the OPCM 3274 (2003) updated till the last version issued in 2005 [OPCM 3431 2005]
The novelties introduced in the seismic design of buildings has been integrated into a general structural code
in 2005 reedited at the very beginning of 2008 [DM 140108 2008] The rationales for the definition of
vertical wind and earthquake loading including the load combinations are the same that can be found in the
Eurocodes with differences found only in the definition of some parameters The seismic design is based on
the assumption of 4 main seismic area (see Figure 20) characterized by values of peak ground acceleration
(with a probability of exceedance equal to 10 in 50 years) equal to 035g (seismic zone 1) 025g (seismic
zone 2) 015g (seismic zone 3) and 005g (seismic zone 4) Actually the basic values for the construction of
the elastic response spectra are given on the basis also of detailed microzonation maps The calculation of
the seismic action for buildings with different importance factors is made explicit as the code require
evaluating the expected building life-time and class of use on the bases of which the return period for the
seismic action is calculated In the microzonation maps anchorage values for the definition of the spectra
are given also with reference to the different return periods and probability of exceedance
In Germany the adaptation of the national structural codes to the Eurocodes started in the field of wind
loadings (DIN 1055-4 Action on structures - Part 4 Wind loads (2005-03)) and seismic loadings (DIN 4149
Buildings in German earthquake areas - Design loads analysis and structural design of buildings (2005-04))
For the design of masonry the partial safety factor concept was introduced into practice in January 2005 with
the new standard DIN 1053-100 Design on the basis of semi-probabilistic safety concept (08-2004)
The wind loadings increased compared to the pervious standard from 1986 significantly Especially in
regions next to the North Sea up to 40 higher wind loadings have to be considered
The seismic design is based on the assumption of 3 main seismic area characterized by values of design
(peak) ground acceleration (with a probability of exceedance equal to 10 in 50 years) equal to 004g
(seismic zone 1) up to 008g (seismic zone 3)
In Portugal the definition of the design load for the structural design of buildings has been made accordingly
to the national code for the safety and actions for buildings and bridges (RSA) In the recent few years a
process to the adaptation to the European codes has also been started The calculation of the design loads
are to be designed according to EN 1991 and EN 1998 Concerning the seismic action a national annex is
under preparation where new seismic zones are defined according to the type of seismic action For close
seismic action three seismic areas are defines with peak ground acceleration (with a probability of
exceedance equal to 10 in 475 years) of 017g (seismic zone 1) 011g (seismic zone 2) and 008g
(seismic zone 3) For a distant seismic load five zones are defined corresponding to a peak ground
acceleration of 025g (seismic zone 1) 020g (seismic zone 2) and 015g (seismic zone 4) 010g (seismic
zone 2) and 005g (seismic zone 5) see Figure 20
Design of masonry walls D62 Page 26 of 106
Figure 19 Seismic zones and wind zones in Germany [after DIN 1055-4 (2005-03) and DIN 4149 (2005-04)]
Figure 20 Seismic zones in Italy (left after OPCM 3274) and in Portugal (rigth)
Design of masonry walls D62 Page 27 of 106
42 STRUCTURAL BEHAVIOUR
421 Vertical loading
This section covers in general the most typical behaviour of loadbearing masonry structures In these
buildings the masonry walls and piers usually support concrete floor slabs and the roof structure without
any separate building frame The masonry walls thus have to carry significant vertical loading (dead and live
load) in addition to their own weight and their sizes are usually determined by their capacity to resist vertical
load In other words they rely on their compressive load resistance to support other parts of the structure
The vertical loading can consist in uniformly distributed loads over the top edge of the masonry walls but
there can also be concentrated loads and effects arising from composite action between walls and lintels and
beams
Buckling and crushing effects which depend on the wall slenderness and interaction with the elements the
wall supports determine the compressive capacity of each individual wall Strength properties of masonry
are difficult to predict from known properties of the mortar and masonry units because of the relatively
complex interaction of the two component materials However such interaction is that on which the
determination of the compressive strength of masonry is based for most of the codes Not only the material
(unit and mortar) properties but also the shape of the units particularly the presence the size and the
direction of the holes influences the compressive strength of the masonry [Lawrence and Page 2004]
422 Wind loading
Traditionally masonry structures were massively proportioned to provide stability and prevent tensile
stresses In the period following the Second World War traditional loadbearing constructions were replaced
by structures using the shear wall concept where stability against horizontal loads is achieved by aligning
walls parallel to the load direction (Figure 21)
Figure 21 Shear wall concept and box-type structural system [after Schneider and Dickey]
Design of masonry walls D62 Page 28 of 106
Lateral forces are therefore transmitted to the lower levels by in-plane shear When combined with the use of
concrete floor systems acting as diaphragms this produces robust box-like structures with the capacity to
resist horizontal load For these structures the walls subjected to face loading must be designed to have
sufficient flexural resistance and the shear walls must have sufficient in-plane resistance The infill masonry
walls in framed buildings are designed for out-of-plane action only [Lawrence and Page 1999]
423 Earthquake loading
In buildings subjected to earthquake loading the walls in the upper levels are more heavily loaded by seismic
forces because of dynamic effects and are therefore more susceptible to damage caused by face loading
The resulting damage is consistent with that due to wind or other out-of-plane loading Shear failures are
more likely to occur in the lower storeys where horizontal in-plane forces are greatest and are characterised
by stepped diagonal cracking Still at the lower storeys in-plane flexural failure can occur This failure is
characterized by the yielding of vertical reinforcement (in reinforced masonry) and crushing of the
compressed masonry toes These failure modes do not usually result in wall collapse but can cause
considerable damage [Lawrence and Page 1999] The flexuralshear failure mode is to a large extent
defined by the aspect ratio (geometry) of the wall the ratio of vertical to horizontal load applied and the
strength of the materials [Tomazevic 1999] Because of higher displacement and energy dissipation
capacity in-plane flexural failure mode are preferred and according to the capacity design should occur
first Shear damage can also occur in structures with masonry infills when large frame deflections cause
load to be transferred to the non-structural walls Both plan and elevation symmetry is desirable to avoid
torsional and softstorey effects Compact plan shapes behave better than extended wings If irregular
shapes cannot be avoided then more detailed earthquake analysis may be necessary According to the EN
1998-1-1 for a building to be categorised as being regular in plan the following conditions should be
satisfied
1- With respect to the lateral stiffness and mass distribution the building structure shall be approximately
symmetrical in plan with respect to two orthogonal axes
2- The plan configuration shall be compact ie each floor shall be delimited by a polygonal convex line If in
plan set-backs (re-entrant corners or edge recesses) exist regularity in plan may still be considered as being
satisfied provided that these setbacks do not affect the floor in-plan stiffness and that for each set-back the
area between the outline of the floor and a convex polygonal line enveloping the floor does not exceed 5
of the floor area
3- The in-plan stiffness of the floors shall be sufficiently large in comparison with the lateral stiffness of the
vertical structural elements so that the deformation of the floor shall have a small effect on the distribution of
the forces among the vertical structural elements In this respect the L C H I and X plan shapes should be
carefully examined notably as concerns the stiffness of the lateral branches which should be comparable to
that of the central part in order to satisfy the rigid diaphragm condition The application of this paragraph
should be considered for the global behaviour of the building
Design of masonry walls D62 Page 29 of 106
4- The slenderness λ = LmaxLmin of the building in plan shall be not higher than 4 where Lmax and Lmin are
respectively the larger and smaller in plan dimension of the building measured in orthogonal directions
5- At each level and for each direction of analysis x and y the structural eccentricity eo and the torsional
radius r shall be in accordance with the two conditions below which are expressed for the direction of
analysis y
eox le 030 rx (414a)
rx ge ls (414b)
where eox is the distance between the centre of stiffness and the centre of mass measured along the x
direction which is normal to the direction of analysis considered rx is the square root of the ratio of the
torsional stiffness to the lateral stiffness in the y direction (ldquotorsional radiusrdquo) and ls is the radius of gyration of
the floor mass in plan (square root of the ratio of (a) the polar moment of inertia of the floor mass in plan with
respect to the centre of mass of the floor to (b) the floor mass)
Still according to the EN 1998-1-1 for a building to be categorised as being regular in elevation the following
conditions should be satisfied
1- All lateral load resisting systems such as cores structural walls or frames shall run without interruption
from their foundations to the top of the building or if setbacks at different heights are present to the top of
the relevant zone of the building
2- Both the lateral stiffness and the mass of the individual storeys shall remain constant or reduce gradually
without abrupt changes from the base to the top of a particular building
3- In framed buildings the ratio of the actual storey resistance to the resistance required by the analysis
should not vary disproportionately between adjacent storeys
4- When setbacks are present the following additional conditions apply
a) for gradual setbacks preserving axial symmetry the setback at any floor shall be not greater than 20 of
the previous plan dimension in the direction of the setback (see Figure 22a and Figure 22b)
b) for a single setback within the lower 15 of the total height of the main structural system the setback
shall be not greater than 50 of the previous plan dimension (see Figure 22c) In this case the structure of
the base zone within the vertically projected perimeter of the upper storeys should be designed to resist at
least 75 of the horizontal shear forces that would develop in that zone in a similar building without the base
enlargement
c) if the setbacks do not preserve symmetry in each face the sum of the setbacks at all storeys shall be not
greater than 30 of the plan dimension at the ground floor above the foundation or above the top of a rigid
basement and the individual setbacks shall be not greater than 10 of the previous plan dimension (see
Figure 22d)
Design of masonry walls D62 Page 30 of 106
Figure 22 Criteria for regularity of buildings with setbacks
Design of masonry walls D62 Page 31 of 106
43 MECHANISM OF LOAD TRANSMISSION
431 Vertical loading
Ideally the vertical loadings have to be transmitted directly to the foundation Generally it is recommended to
avoid any secondary support construction eg beams as their vertical stiffness leads to problems especially
under seismic loadings
432 Horizontal loading
The distribution of the horizontal loadings ndash eg from wind or seismic action ndash to the shear walls is deciding
for the behaviour of the structure On the one hand it is necessary to ensure a proper load distribution in
combination with possible redundancies (redistribution) by a stiff slab and on the other hand an in-plane
restraint leads to more favourable boundary conditions of the shear walls Therefore the structural system as
a cantilever beam is generally too unfavourable describing a shear wall in a common construction
The calculated horizontal loadings of each shear wall can be redistributed according to EN 1996-1-1 2005
553 (8) Here a reduction up to 15 is allowed if the load on a parallel shear wall is increased
correspondingly and assuming equilibrium
Figure 23 Spacial structural system under combined loadings
Design of masonry walls D62 Page 32 of 106
Figure 24 Horizontal system of the shear wall with different restraints into the RC storey slabs
433 Effect of openings
Openings influence the stiffness of in-plane loaded shear walls and the corresponding stress distribution
significantly The effects can be calculated using a finite-element-programme assuming al linear-elastic
behaviour of the material The shear modulus should be fixed to 40 of the E-modulus For the design
process wall can be separated into stripes
Figure 25 Effect of opening on the structural idealization for out-of-plane-loadings
For the out-of plane loaded walls the effect of openings can be handled by idealizing the walls as several
combinations of horizontal and vertical strips Additional constructive arrangements have to be kept eg
extra reinforcement in the corners (diagonal and orthogonal)
Design of masonry walls D62 Page 33 of 106
Figure 26 Effect of opening on the structural idealization for out-of-plane-loadings [MDG-4]
Design of masonry walls D62 Page 34 of 106
5 DESIGN OF WALLS FOR VERTICAL LOADING
51 INTRODUCTION
According to the EN 1996-1-1 and to most of the structural codes when analysing walls subjected to vertical
loading allowance in the design should be made not only for the vertical loads directly applied to the wall
but also for second order effects eccentricities calculated from a knowledge of the layout of the walls the
interaction of the floors and the stiffening walls and eccentricities resulting from construction deviations and
differences in the material properties of individual components The definition of the masonry wall capacity is
thus based not only on the compressive strength but also on the slenderness ratio of the walls and on their
typical boundary conditions These consist in walls restrained only at the top and bottom or can be improved
by restrains also on the vertical edges (one or both) Once the eccentricity is known it can be used to
evaluate reduction factors for the compressive strength of the masonry walls and carry out axial load
verifications or it can be used to carry out out-of-plane bending moment verifications of the wall sections
Design of masonry walls D62 Page 35 of 106
52 PERFORATED CLAY UNITS
521 Geometry and boundary conditions
Prior to the definition of the design strategy based on the out-of-plane moment of resistance due to the
presence of the reinforcement or on the reduction of vertical load capacity as it is made for unreinforced
masonry in the case of walls with slenderness ratio λ gt 12 it is necessary to define the effective height hef
and the effective thickness tef of the walls where λ = hef tef based on the boundary conditions of the walls
The selected boundary conditions are some of the typical conditions listed in section sect 51 and given by the
EN 1996-1-1 (2005) walls restrained at the top and bottom by reinforced concrete floors or roofs spanning
from both sides at the same level or by a reinforced concrete floor spanning from one side only and having a
bearing of at least 23 of the thickness of the wall and with eccentricity smaller than 025 times the thickness
of the wall walls restrained at the top and bottom by timber floors or roofs spanning from both sides at the
same level or by a timber floor spanning from one side having a bearing of at least 23 the thickness of the
wall but not less than 85 mm (in our case more in general deformable roofs) walls restrained at the top and
bottom and stiffened on one vertical edge walls restrained at the top and bottom and stiffened on two
vertical edges
The effective thickness tef of single-leaf walls should be taken as the actual thickness of the wall t unless
the wall is stiffened by piers In that case the effective thickness is measured as
tef = ρt t (51)
where the stiffness coefficient ρt is found as explained in Table 10 and Figure 27
Table 10 Stiffness coefficient ρt for walls stiffened by piers see Figure 27 [after EN 1996-1-1]
Figure 27 Diagrammatic view of the definitions used in Table 10 [after EN 1996-1-1]
Design of masonry walls D62 Page 36 of 106
In the analyzed cases the effective thickness of the wall has been taken as the actual thickness The
effective height hef of single-leaf walls should be taken as the actual height of the wall h times a reduction
factor ρn that changes according to the above mentioned wall boundary conditions
hef = ρn h (52)
For walls restrained at the top and bottom by reinforced concrete floors or roofs spanning from both sides at
the same level or by a reinforced concrete floor spanning from one side only and having a bearing of at least
23 of the thickness of the wall and unless the eccentricity is greater than 025 times the thickness of the
wall ρ2 = 075 (otherwise and for wooden floors ρ2 = 10) For walls restrained at the top and bottom and
stiffened on one vertical edge (with one free vertical edge)
if hl le 35
(53a)
if hl gt 35
(53b)
For walls restrained at the top and bottom and stiffened on two vertical edges
if hl le 115
(54a)
if hl gt 115
(54b)
These cases that are typical for the constructions analyzed have been all taken into account Figure 28
gives the slenderness ratios for walls with different height to thickness ratio in case that the walls are not
restrained at the vertical edges In the case of eccentricity of the vertical load due to floors smaller than 025
times it can be seen that λ le 12 for the ALAN masonry system but with deformable roofs λ becomes major
than 12 for the CISEDIL system Figure 29 shows the reduction factors for the evaluation of the effective
height for walls restrained at the vertical edges varying the height to length ratio of the wall The
corresponding slenderness ratios are given in Figure 30 and Figure 31 It can be see that obviously if the
walls are restrained by stiff roofs and are stiffened at one or two vertical edges the slenderness ratio is even
more reduced (case of the ALAN system) In the case of deformable roofs if the walls are restrained on two
vertical edges or are restrained on only one vertical edge but with length of the wall le 35 m the
slenderness is reduced to λ le 12 also for the CISEDIL system This case thus cover most of the practical
application therefore for the design the out of plane bending moment of resistance should be evaluated
Design of masonry walls D62 Page 37 of 106
Slenderness ratio for walls not restrained at the vertical edges
0
2
4
6
8
10
12
14
16
18
50 54 58 62 66 70 74 78 82 86 90 94 98 102
106
110
114
118
122
126
130
134
138
142
146
150
154
158
162
166
170 ht
λ
λ2 (e le 025 t)λ2 (e gt 025 t)
wall h = 2700 mm t = 300 mmeccentricity of load lt 025 t
wall h = 6000 mm t = 380 mmdeformable roof
Figure 28 Slenderness ratios for walls not restrained at the vertical edges(varying the height to thickness
ratio)
Reduction factors for the evaluation of the eccentricity for walls restrained at the vertical edges
00
01
02
03
04
05
06
07
08
09
10
053
065
080
095
110
125
140
155
170
185
200
215
230
245
260
275
290
305
320
335
350
365
380
395
410
425
440
455
470
485
500 hl
ρ
ρ3 (e le 025 t)ρ3 (e gt 025 t)ρ4 (e le 025 t)ρ4 (e gt 025 t)
Figure 29 Reduction factors for the evaluation of the effective height for walls restrained at the vertical
edges (varying the wall height to length ratio)
Design of masonry walls D62 Page 38 of 106
Slenderness ratio for walls restrained at the vertical edges
Figure 98 Design chart M x N for UMINHO reinforced masonry system (Variation of vertical reinforcement ratio HL=050) (a) HL = 050 (b) HL = 070 (c) HL = 100 (d) HL = 175 and (e) HL = 350
Design of masonry walls D62 Page 101 of 106
8 OTHER DESIGN ASPECTS
81 DURABILITY
For the durability of reinforced masonry the corrosion of the reinforcement is the relevant issue Generally it
can be solved using corrosion resistant steel (not considered here) or by adequate protection (place in
mortar place in concrete zinc coating) According to the local exposure conditions (climate conditions
moisture) the level of protection for reinforcing steel has to be determined
The demands are give in the following table (EN 1996-1-1 2005 433)
Table 25 Protection level for the reinforcement steel depending on the exposure class
(EN 1996-1-1 2005 433)
82 SERVICEABILITY LIMIT STATE
The serviceability limit state is for common types of structures generally covered by the design process
within the ultimate limit state (ULS) and the additional code requirements - especially demands on the
minimum strength of the materials (units mortar infill reinforcement) and the minimum reinforcement ratio
Also the minimum thickness (corresponding slenderness) has to be checked
Relevant types of construction where SLS might become relevant can be
Design of masonry walls D62 Page 102 of 106
bull Very tall exterior slim walls with wind loading and low axial force
=gt dynamic effects effective stiffness swinging
bull Exterior walls with low axial forces and earth pressure
=gt deformation under dominant bending effective stiffness assuming gapping
For these types of constructions the loadings and the behaviour of the structural elements have to be