SEISMIC RESPONSE AND REHABILITATION OF HISTORIC MASONRY BUILDINGS Dissertation submitted as part requirement for the Degree of Master of Science in Earthquake and Civil Engineering Dynamics BY FRANCISCO ROBERTO TRUJILLO LEON Supervisor: Prof. Kypros Pilakoutas The University of Sheffield Department of Civil and Structural Engineering September 2007
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SEISMIC RESPONSE AND REHABILITATION OF
HISTORIC MASONRY BUILDINGS
Dissertation submitted as part requirement
for the Degree of Master of Science in
Earthquake and Civil Engineering Dynamics
BY
FRANCISCO ROBERTO TRUJILLO LEON
Supervisor:
Prof. Kypros Pilakoutas
The University of Sheffield
Department of Civil and Structural Engineering
September 2007
ii
Declaration Statement
The author certifies that all the material within the thesis titled Seismic Response and
Rehabilitation of Historic Masonry Buildings is his work except where it its clearly
referenced to others.
Francisco Roberto Trujillo Leon
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Abstract
Historic masonry buildings in seismic areas are very vulnerable because they have
not been explicitly designed to withstand seismic forces. The assessment of their seismic
behaviour is very important to planning the correct rehabilitation strategies for the
improvement of their resistance during seismic events. This dissertation presents a procedure
for assessing the safety of historic masonry buildings under seismic vibrations based on
measurements of their natural frequencies, numerical simulations and failure mechanisms in
order to recommend the best rehabilitation technique.
As example a case study of the seismic behaviour of the Santo Domingo Church,
located in México, is included. For this purpose, a model of the historic masonry building
was created using the finite element basis.
The geometrical configuration of the church is as follows: the plan view inscribes a
cross (67.50m x 43.70m) with walls of 2.0m to 3.0m in depth, and vaulted roof; in the
connection a big cupola communicates with adjacent modules. In the first section of the
building two towers take part over the main facade, with 27.46m in high. The numerical
solutions obtained from the distinct element analysis are validated by comparing the results
with those obtained from the existing works (Mistler, Butenweg, & Meskouris, 2006; &
Meli, 1998) and by measurement of its natural frequencies and failure comparison with the
real structure.
The two seismic analyses performed on the structure reveals a brittle failure in wall
to wall connections of the main facade with the vaulted body, a possible cracking in middle
span of the vaulted roof and collapse of the towers by excessive tensional stresses. These
results are related to the elastic linear behaviour of the structure and should be considered
even more critical because nonlinear issues as crack, sliding and disconnections were no
measured in the structure. It is suggested the use of GFRP reinforcement in both intrados and
extrados faces of the vaulted area and the use of CFRP reinforcement bars as connections
between the towers and its base.
The conclusion of this assessment is that even when the finite element method
presents a revolutionary tool for the assessment of any structure, needs the application of
interdisciplinary tests to be confirmed as representative. Never must be considered as a
duplicate of the real behaviour and some engineering judgement is always necessary for the
correct interpretations of the results.
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Acknowledgements
I would like to thanks to my supervisor Prof. Kypros Pilakoutas for his guidance andsupportive analysis.
Particularly I really want to thank to my parents for all their support during all thistime without which I would not be able to study this degree.
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Table of Contents
Declaration Statement ........................................................................................... ii
Acknowledgements ............................................................................................... iii
Abstract .................................................................................................................. iv
APPENDIX A: Letter of Venice, ICOMOS recommendations.
APPENDIX B: Drawings of the structure.
APPENDIX C: Seismic properties tables.
APPENDIX D: Time history analysis results.
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List of Figures
Figure 2- 1 Flowchart with the methodology for structural interventions proposed byICOMOS. ..........................................................................................................................16
Figure 2- 6 Load condition in a column (Section of St. John's Chapel showing Vaults,Adapted from Bond, Gothic Architecture, p283).................................................................23
Figure 2- 7 (a)Schematic illustration of an arch. 1.Keystone, 2.Voussoir, 3.Back, 4.Impost,5.Intrados, 6.Rise, 7.Bay, 8.Abutment. (Messer Woland), (b)Arch supported by a leaningbuttress. (Block, Ciblac, & Ochsendorf, 2006) ....................................................................24
Figure 2- 8 View of a barrel vault from above showing forces developed by the static system. ..........................................................................................................................................25
Figure 2- 9 Dome on pendentive (Totya). ...........................................................................26
Figure 2- 10 Case 1. Contours of damage variables at failure. (a)Tensile damage.(b)Compressive damage. (Berto, 2005)...............................................................................28
Figure 2- 11 Case 2. Contours of damage variables at failure. (a)Tensile damage.(b)Compressive damage. (Berto, 2005)...............................................................................29
Figure 2- 12 Failure modes of masonry panels. (M. Mistler & C. Butenweg & K. Meskouris,2006) .................................................................................................................................30
Figure 2- 13 Four-hinge failure mechanism of a semi-circular masonry arch submitted to anasymmetrical loading (Oliveira, 2006) ................................................................................31
Figure 2- 14 (1)Failure of a building corner, (2)Out of plane collapse of a bearing wall,(3)Partial collapse due to the thrust of the roof and bad connection tie beam-wall,(4)Separation of the two leaves of a wall, (5)Shear failure of a wall. (Penazzi, 2001) ..........33
Figure 2- 15 Different FEM approaches for modelling masonry. (M. Mistler & C. Butenweg& K. Meskouris, 2006) .......................................................................................................40
Figure 2- 16 Impact on masonry of using (a)Repointing with soft mortar. (b)Repointing withhard mortar. (Pearson, 2007) ..............................................................................................42
Figure 2- 18 (a)Reinforcement of vault with mortar. (b)Reinforcement with reinforcedconcrete. ............................................................................................................................47
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Figure 2- 19 Summary for the full length CFRP reinforcement at the intrados and extrados.(Basilio, Oliveira, & Lourenco, 2004). ...............................................................................48
Figure 3- 1 The front entry of the Church of Santo Domingo de Guzman in San Cristobal deLas Casas. (Agguizar) ........................................................................................................50
Figure 3- 2 Plan section of the Santo Domingo Cathedral ...................................................51
Figure 3- 3 Main facade of the Santo Domingo Church ......................................................52
Figure 3- 4 Historic materials distribution ..........................................................................53
Figure 3- 5 (a)Finite Element model of a single arch, (b)Discretization of the model...........55
Figure 3- 7 Analytical model of the structure. .....................................................................56
Figure 3- 8 Grouting work .................................................................................................57
Figure 3- 9 Restitution works effectuated in the past ..........................................................58
Figure 3- 10 (a)Joints location into the numerical model. (b)Sections distribution. ..............59
Figure 3- 11 Principal maximum (a) and minimum (b) stresses under dead load. ................59
Figure 3- 12 (a)Principal compressive stresses under dead load. (b)Principal stresses of mainarches under dead load. ......................................................................................................60
Figure 3- 13 (a) First mode of vibration (T=0.28sec). (b) Second mode of vibration(T=0.23sec). .......................................................................................................................61
Figure 3- 14 Third mode of vibration (T=0.23sec) ..............................................................62
Figure 3- 15 Fourth mode of vibration (T=0.22sec). ...........................................................62
Figure 3- 16 Response Spectrum according to NTC. ...........................................................63
Figure 3- 17 (a)Shear stress diagram and deformed shape. (b)Stress diagram underearthquake loading in principal direction. ...........................................................................64
Figure 3- 18 (a)Principal stresses in Y-direction due to earthquake. (b)Principal stresses inX-direction due to earthquake.............................................................................................65
Figure 3- 19(a)Displacement contours originated by the design spectra in Y-direction.(b)Displacement contours originated by the design spectra in X-direction(Contours in cms). ..........................................................................................................................................65
x
Figure 3- 20 (a) 1995 earthquake accelerograms in N-S direction (b) 1995 Earthquakeaccelerograms in E-W direction..........................................................................................66
Figure 3- 21 (a)Stresses diagram in Y-direction [95 Earthquake]. (b)Stresses diagram in X-direction [95 Earthquake]. ..................................................................................................67
Figure 3- 22 (a)Stresses diagram in X-direction [95 Earthquake]. (b)Maximum envelop ofstresses in X-direction [95 Earthquake]. .............................................................................67
Figure 3- 23 (a)Stresses diagram in Y-direction [95 Earthquake]. (b)Stresses diagram in Y-direction [95 Earthquake]. ..................................................................................................68
Figure 3- 24 Maximum envelop of principal stresses in X-direction [95 Earthquake]. .........68
Figure 3- 25 (a) Maximum envelop of principal stresses in Y-direction. (b) Deformed shapeunder recorded accelerations [95 Earthquake]. ....................................................................69
Figure 3- 26 (a)Displacement contours originated by the design spectra in X-direction.(b)Displacement contours originated by the design spectra in Y-direction(Contours in cms). ..........................................................................................................................................69
Figure D- 1 Displacement in X-direction of joint 588 (orange) and 579 (blue) VS time.......89
Figure D- 2 Displacement in X-direction of joint 591 (green) and 578 (blue) VS time. .......90
Figure D- 3 Displacement in Y-direction of joint 588 (orange) and 579 (blue) VS time.......91
Figure D- 4 Displacement in Y-direction of joint 591 (green) and 578 (blue) VS time. .......92
Figure D- 5 Response spectrum curve for joint 1365 matching with the third mode of thestructure at 0.23sec Period vs. Pseudo spectral acceleration in Y-direction. .........................93
Figure D- 6 Response spectrum curve for joint 591 matching with the first mode of thestructure at 0.3sec Period vs. Pseudo spectral acceleration in Y-direction. ...........................94
The main difficulty to determine the structure response and failure mechanisms
comes from the variability of the materials, mechanical properties and building techniques
applied during construction.
According to Mistler, Butenweg, & Meskouris, (2006) a masonry wall can fail in
different ways.
· Shear failure. Characterized by cracks in the mortar and where the case of a strong
mortar – low strength brick is presented, the cracks simply bisect the bricks (Figure
2-11(a)).
· Friction failure. This type of failure is presented when a strong lateral load is applied
to the structure in combination to the low vertical loads of the structure (Figure 2-
11(b)).
· Bending failure. This occurs when the sections are slender in relation with the
vertical loads (Figure 2-11(c)).
Figure 2- 12 Failure modes of masonry panels. (M. Mistler & C. Butenweg & K. Meskouris, 2006)
“The majority of these problems may occur due to decay of masonry materials and
subsequent weakening of the structures, the weak tensile and shear strength of unreinforced
masonry and the inadequate interconnection of the masonry elements” (Hassapis, 2000).
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2.5.2 Historic masonry arches
For semicircular masonry arches without reinforcement under the application of a
concentrated load at the quarter span, four plastic hinges are expected to appear (Figure 2-
12) (Heyman, 1982).
Figure 2- 13 Four-hinge failure mechanism of a semi-circular masonry arch submitted to an asymmetricalloading (Oliveira, 2006)
An arched masonry structure maintains compression as long as the thrust line
(pressure line) is kept inside the central core. This line represents the compressive force at
each cross-section. When the pressure line moves outside the section, this sections becomes
in tension and the formation and consequent opening of a crack takes place, forming a plastic
hinge at the compressed edge of the arch.
By the using of a bonded FRP reinforcement, the formation of a fourth hinge
mechanism is prevented. Therefore, only three hinges are able to rise, transforming the arch
into an isostatic structure.
In this case four new failure mechanisms are likely to occur (Basilio, Oliveira, &
Lourenco, 2004).
· Shear failure due to sliding along a mortar joint.
· Failure due to masonry crushing.
· Failure due to detachment of the fibbers.
· Failure due to sliding along masonry joint.
Moreover, in addition to the usual stresses parallel to the fibbers, the curved shape of
arches originates stresses with a component normal to the fibbers, which may lead to the
detachment of the reinforcement from masonry (Oliveira, Basilio, & Lourenco, 2006).
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Sliding between the fibbers and its support is usually neglected since shear stresses
at the FRP-masonry interface are of minor magnitude (Valluzzi & Modena, 2006). Also FRP
tensile failure is not likely to occur due to its high tensile strength.
2.5.3 Historic masonry structures
One big disadvantage of historic masonry structures consist in the very low tensile
strength of its constituents triggering in an absence of capacity to transfer tensional forces or
bending moments between adjacent elements. Moreover, the inertial forces are not correctly
transferred to the ideal elements to resist lateral forces.
The shear and tensile forces developed during earthquakes usually result in cracks at
the main body and disconnections of walls in the intersections.
Cracks can develop diagonally and run either partially or completely through the
masonry piers between window openings due to tensile stresses, or horizontally in masonry
piers between window openings due to alternating bending moments or diagonally above the
wall opening due to shearing (Hassapis, 2000).
In addition, for the case of isolated buildings four main mechanisms were identified
for non repaired structures (Penazzi, Valluzi, Saisi, Binda, & Modena, 2001):
1. Out of plane of loadbearing walls with local or total collapse of the facades or of
the corners, or large deformation of the walls. This mechanism is due to the lack of
connection between orthogonal walls (Fig. 2-13(1)) and between walls and floors or roofs
and to the presence of large openings (Fig. 2-13(2)).
2. Out of plane mechanisms with local or large failures of the upper part of the walls
and collapses of parapets, cornices and spandrels. This occurs due to the thrust of the roof
and absence of connection between the roof and the masonry (Fig. 2-13(3)).
3. Wall disconnection and leaf separation with local or global failures. The presence
of in-homogeneities in the wall, the lack of connection between the leaves of multiple leaf
walls (Fig. 2-7(4)), the filling of openings without good connection between the old and the
new parts or the use of different types of materials can be the causes of such mechanism.
4. In plane mechanisms due to shear stresses with diagonal cracks of piers and walls
at the different floors. They are mainly due to: bad positioned openings, differential stiffness
of the walls between openings, presence of weak lintels (Fig. 2-13(5)).
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Figure 2- 14 (1)Failure of a building corner, (2)Out of plane collapse of a bearing wall, (3)Partial collapsedue to the thrust of the roof and bad connection tie beam-wall, (4)Separation of the two leaves of a wall,(5)Shear failure of a wall. (Penazzi, 2001)
The elements that present more risk to collapse in case of seismic events are: slender
towers, columns and isolated walls. According to Meli (1998), the failure mode in towers is
less critical than suspected. During the vibration of these elements a successive process of
opening and closing of cracks is presented by actions, bending and sliding of the joints and
horizontal cracking. Such process dissipates energy increasing the damping in the elements
and reducing any collapse threatens.
2.5.3.1 Problems due to new additions
The addition of new buildings to old ones represents another source of problems
under this category. In particular, (Bidwell, 1977) argues that the following considerations
should take place when new extensions are added to already existing buildings:
· Whether and how to tie the new structure to the old one.
· The effect that this may have on the sub-soil conditions and the foundations.
· Whether they will trigger any direct or indirect stresses to the old structure.
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“Differential settlements are common (due to the addition of new buildings)” (Hassapis,
2000).
2.5.3.2 Problems due to foundation movements
Generally, many historic buildings do not present proper foundations; so, initial
settlements take place in the first years of its life (Cook & Pegram, 1993). However, such
building continues working firmly without compromising the safety of the structure;
normally such changes are likely to stop at an early stage, since structures usually adapt
themselves to their environment reaching to a new equilibrium of internal stresses, especially
when soft mortars were used during the construction of the structure (Feilden, 1994).
Two main sources of foundation movements can be clearly indentified; those
produced by earthquakes and settlements. Earthquake movements generally develop high
stresses into the structure in a short period of time, while for settlement these forces occur in
a long period and due to many causes.
According to Feilden, (1994) common causes responsible for subsidence are the
following:
· Mining nearby the structure;
· Existence of a wall near or underneath the structure;
· Other kinds of excavations near the foundations for purposes of drainage,
construction of basements, etc.;
· Problems caused by trees and creepers;
· Landslides caused by heavy rain, floods, etc.;
· Potholes or caves existing underneath a structure, which have been created by
underground streams;
· Abstraction of groundwater, causing lowering of the water table;
· Rise of the water table, caused by blocked underground water.
· Heavy structures built near old ones, which may change ground strains.
· Vibrations caused by heavy traffic passing from adjacent to an old structure road or
by pile driving operating near the structure.
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· Gradual geological movements.
· Earthquakes
“When unequal settlement of masonry takes place, the appearance of cracks at the walls
is a common result of the in-plane deformations of the walls” (Hassapis, 2000).
2.5.3.3 Problems due to material deterioration
The durability of historic masonry structures is directly relative to its materials.
There are many cases encouraging the decay of materials. The presence of water is one of
the most common and hazardous ones both directly and indirectly, since it can trigger the
development of various other deterioration mechanisms. Water can help to dissolve mortar,
may reduce the strength of masonry units, may result in the decay of timber and iron, may
lead to frost and chemical crystallisation and may encourage chemical attack and organic
growth (Hassapis, 2000).
Cook & Hicks, (1992) argue that the allowed limit before a structure is deemed
unstable due to creep is dependent upon a variety of factors such as the flexibility of the
materials, their individual susceptibility to creep, the tolerance of the joints between the
different components and the interconnection of the structural elements, all of which are
usually more flexible in this type of structures.
There are many ways of crack to appear; due to moisture, thermal movements and
cracking.
2.6 Assessment methods of historic masonry buildings
2.6.1 Introduction
The study of historic masonry structures becomes complicated in that many
variations of materials and building techniques existed in the past without the guidance of
any established regulation. Most of the masonry structures were built on empirical data
based on experience acquire in previous constructions and following the basic interpretations
of nature, without use of any mathematical analysis.
According to Meli (1998), “The quantitative methods used to determine shape,
dimensions and material properties of the elements into a structure that is required to resist
external loads, are relatively recent. In the past, an important source for the development of
new aesthetic shapes was the observation of structures created by nature; the correct
lecture, interpretation and improvement were the base for new structural solutions”.
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Even at present our knowledge about the mechanical behaviour of masonry is not
well known as for other materials and many calculation methods for capacity assessments
hardly ever consider the complex behaviour of masonry as a ‘composite’ material.
During the XX century numerical methods of analysis started to increase in
importance due to the employment of approaching methods that in a simple explanation
consisted in corroboration and adjustment by successive approximations until the error was
considered as despicable. This technique required a huge quantity of calculations, and this
method was not employed until the appearing of powerful computers capable of compute
calculations to unimaginable speeds (Meli & Sanchez-Ramirez, 1993).
Another element that increases the use of this method nowadays is the computed
aided engineering (CAE) packages, capable of solve different types of structures under many
different solicitations. The technique of general application for this purpose is widely known
as the Finite Element Method (FEM), it consists in the division of the structure into sub-
elements for which equilibrium and deformation equations are already assigned; boundary
conditions are established in the joints intersecting to two or more elements (Zienkiewicz &
Taylor, 1967).
2.6.2 Scopes and limitations
In the world there is still a preference for the intuitive a qualitative judgment of
historic monuments; however, for the engineer it is always important the support of
analytical models, as well as laboratory test of the material properties.
As discussed before, during the last decades there has been an important
improvement in the experimental and analytical methods for the studies of historic buildings,
also now we can count with powerful analytical tools that allow us to solve complex
structures with a reasonable computational cost. The weak point in these models is the
application of the procedures to determine the parameters and models that define the
response.
Since the preparation of an analytical model confronts many difficulties, starting
from the identification of the structure itself to the definition of its structural geometry. The
conditions of continuity between different elements are very difficult to establish. In historic
masonry buildings the elements sometimes are only one above the other, and exists a
possibility of rotations in the contact surface. There are some cases where the elements can
not be clearly established as a non-structural or structural component.
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2.6.3 Linear static analyses
It is common to call static methods to those based on the hypothesis in which the
structural material has a linear behaviour, both in tension as compression; the interaction
between the internal deformations and applied stresses increase proportionally. This
hypothesis has allowed to obtain exact solutions for typical structural models, in which, the
equilibrium conditions are satisfied.
However, the behaviour of structural materials is not strictly a linear relationship of
stress-strain deformation; considered acceptable enough for new materials as steel and
concrete, for masonry, nevertheless, the differences are considerable; first, the material has
no strength in tension, by which is subjected to cracking that generates local deformations
and constantly changing in the stress state, this obviously corresponds to a high non-elastic
material. Moreover, masonry is affected by different external agents, as temperature changes,
the diverse deformations in mortar and movement effects in the supports. The big variability
of the material properties from section to section, also changes the stress distribution.
The main objection in the use of the elastic methods is that they don’t recognize the
non-linear behaviour of the masonry.
In summary, accurate results can not be obtained from a static analysis but can be
considered as representative of the structure and be used for the assessing.
2.6.4 Nonlinear static analyses
Nonlinear procedures generally provide a more realistic indication of the demands
on individual components of structures that are loaded significantly beyond their elastic
range of behaviour, than do linear procedures.
Most of the non linear models consider that the properties against tension stresses
are the same than those of compression and that both are invariable against any load. These
limitations are surpassed when in the models the materials are linear in compression, but
have zero strength in tension. The solution of these models requires a nonlinear analysis
method, because the level of load is increased, the size of area under tension increase,
becoming necessary to modify the characteristics of the model during time (Berto, Saetta,
Scotta, & Vitaliani, 2005).
They are particularly useful in that they provide for (Petkovski, 2007):
• More realistic estimates of force demands on potentially brittle components (force-
controlled actions), such as axial loads on columns and braces.
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• More realistic estimates of deformation demands for elements that must deform
inelastically in order to dissipate energy imparted to the structure by ground motions.
• More realistic estimates of the effects of individual component strength and
stiffness degradation under large inelastic demands.
• More realistic estimates of inter-story drifts that account for strength and stiffness
discontinuities that may develop during inelastic response.
• Identification of critical regions in which large deformation demands may occur
and in which particular care should be taken in detailing for ductile behaviour.
• Identification of strength discontinuities in plan or elevation that can lead to
changes in dynamic characteristics in the inelastic range.
2.6.5 Dynamic analyses
The calculus of the effects over the structures produces external variations; it is
considered that the last has constant values in time (that proceed in static form). This is valid
for its own weight and for some solicitations as differential movements and contraction due
to changes in temperature.
Nevertheless, there are situations in which is important to do a dynamic analysis in
historic masonry, for example when there are high frequency vibrations, induced by traffic or
vibratory equipment, and the seismic response in situations in which the dynamic effect
results important at a local or global level.
Probably the must important tool for dynamic analyses can be the eigenfrequencies
and modal shapes. This allows evaluating the importance of the dynamic effects induced by
external agents.
To solve this, preference has been given to the employment of dynamic elastic
analyses, where the stiffness properties are modified manually. As a result, many
methodologies have been proposed, see (Ramos & Lourenco, 2005; Mistler, Butenweg, &
Meskouris, 2006 and Cardoso, Lopes, & Bento, 2005), where the modifications are guessed
from the result of the first analysis and results are compared according to the seismic
vulnerability of the structure.
2.6.6 Numerical modelling
For the structural modelling of masonry historic buildings the use of a three-
dimensional finite element model become necessary to obtain accurate results. This
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numerical analysis is also found to be questionable due to many factors: the anisotropy and
decay of the constitutive materials, the fact that consists of two materials with different
properties and without any tensional strength. These factors trigger the developing of cracks
at any section affecting the global characteristics of the element. But, in spite of many
uncertainties, though, numerical models are considered as a very useful tool that used in
combination with experimental work can be very effective in the assessment of historic
masonry buildings.
The first attempt for the analytical treatment of monuments built of fitted stones
under dynamic excitation was presented by Housner (1963).
In actuality, to carry out a structural analysis for old masonry structures, many
engineers model the materials linked to linear behaviour without consider the whole complex
performance of masonry (as a composite material with anisotropic properties). This method
does not describe a realistic performance of the structure but, as stated before, gives an idea
about the main causes of failure and its more accessible and less cost-time consuming in
comparison with other methods, e.g. non-linear micro-models.
Lourenco (2005) point out that it is essential to verify the adequacy of the models
with the existing building; this can be carried out with different techniques, mainly flat-jack
testing or dynamic identification, but also a comparison with the damage survey (cracks,
displacements) is allowed.
According to (Syrmakezis, Asteris, & Mavrouli, 2006), the young’s modulus of
elasticity, E, is a parameter that determinatively influences the masonry’s response. For
micro-analysis purposes, materials are assigned with a value that can be determined from
experimental, destructive or non-destructive testing. For macro-analysis the value is selected
either using proper equations or as explained in chapter 2.5.1 by analytical evaluation of a
masonry block, for a model consisting of two blocks and a mortar joint.
2.6.6.1 Finite element method
The finite element method of analysis makes use of different finite elements: One-
dimensional (bar, frames), Two-dimensional (shell, plate, membrane) and Three-dimensional
(solid). For the simulation of the influence of composite materials in the structure, micro or
macro-analysis can be used, depending on the accuracy desired. During micro-analysis,
blocks, mortar and the interface are simulated separately simulating the contact nonlinearity,
while for macro-analysis, a homogeneous material represent the masonry behaviour. The
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deformability in this type of models is considered by discretization of the mesh into finite
elements.
There are different approaching techniques to model a composite masonry structure
based on the finite element method (Figure 2-14). In the first one, each brick, mortar and
boundary are modelled by separated, so a large number of micro-models are produced to
simulate the nonlinear behaviour of each element. For the second, the bricks and the
boundaries are modelled together so the grout elements (mortar) are assumed of zero
thickness. This model is computationally less demanding and allows to be used on large
structures under dynamic loads. For this model the global behaviour has to be defined.
For the first previous mentioned approaching method, the accuracy found in the
results is very high, but is very expensive computationally speaking been suitable only for
small elements.
Figure 2- 15 Different FEM approaches for modelling masonry. (M. Mistler & C. Butenweg & K. Meskouris,2006)
2.7 Seismic safety
The historic masonry buildings are mainly very heavy and structurally stiff.
Therefore, high inertia forces that depend on the product of the mass and acceleration are
generated. As a result, the frequency of the vibration modes is typically between 1 and 4 Hz;
located in the interval where the dominant frequencies of dominant earthquakes are found
(Meli, 1998). Moreover, Cardoso, Lopes, & Bento, (2005) argued that a far distance
earthquake, with low frequency contents, is the one that induces higher accelerations to this
type of structures. This directs us to observe that the accelerations presented in this type of
buildings are very elevated and the damages are considerable.
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As result, the masonry in historic buildings has a nonlinear anisotropic behaviour
and a post-peak load-carrying capacity, perhaps one of the keys to why buildings sometimes
withstand seismic load far beyond of its considered limits. So, the overall behaviour of
historic masonry structures is brittle and nonlinear.
The concept of redundancy is extremely important to the design of structures for
seismic resistance and a very important point to be taken into account for the assessment of
historic masonry buildings. In a redundant structure, multiple elements (or components) will
be available to resist forces induced. Individual components of the structure will be strained
beyond their elastic range. As this occurs, the structure starts to experience damage in the
form of cracking, spalling, buckling, and yielding of the various components. As
components become damaged, they degrade in stiffness, and some elements will begin to
lose their strength. All the brittle elements into the structure are not able to sustain inelastic
deformations and will fail suddenly (Petkovski, 2007).
Architectural walls and partitions can affect the stiffness of structural elements and
also introduce soft story and torsional conditions into otherwise regular buildings. Therefore,
many engineers having this in mind add extra lumped masses to simulate the effect of non-
structural elements in the total behaviour.
Obviously an analytical refinement does not eliminates the considerations previously
commented and must be taken into account for this type of structures, in particular in historic
masonry buildings; where the elegance and apparent perfection of the finite element method
can make to loose contact with the real structure.
2.8 Rehabilitation methods
According to Pearson (2007), rehabilitation interventions in historic masonry
structures can be classified into two concepts. First, the repair concept; carried out for
structures in which the deficiencies are related to isolated structures with typical modes of
failure, known to cause a poor earthquake performance in the past. This is based on the
insertion of new materials into parts of the existing historic masonry. Second, the
strengthening concept; a process in which a complete analysis of the structure is performed,
here the objectives are checked for adequacy to resist strength and deformation demands
against different solicitations; mainly those derived from earthquakes.
During any rehabilitation work special care most be taken for discontinuity in the
flow of forces, alterations in the existing structural systems and local differences in rigidity
could lead to shifts in load transfer that inevitably become into cracks.
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There are numerous techniques aiming to the consolidation of decayed masonry
structures and materials.
When working on historic and, in particular, listed structures, repairs should ideally
be carried out using similar materials to the original. Not only are more appropriate to the
historic character of the architecture, but they usually work better than modern alternatives,
especially when used in conjunction with other traditional materials and construction
techniques (Bennett, 2002).
2.8.1 Repointing
According to (Ashurst, 1988c) pointing is the process of filling the outer part of the
joints between masonry units, where the bedding mortar has been deliberately left or raked
back from the surface or where the original mortar has weathered.
Repointing represents an important repair method in historic buildings, because it
can radically change the character and appearance of the structures and protect them from
various causes of decay.
The selection of the appropriate mortar becomes a very important issue in the
effectiveness of this technique. A soft mortar than the units can absorb stresses developed
through movements of the adjacent masonry, while a hard mortar will produce cracks
between mortar and bricks or will cause spalling (Figure 2-15).
Figure 2- 16 Impact on masonry of using (a)Repointing with soft mortar. (b)Repointing with hard mortar.(Pearson, 2007)
“Repairs using inappropriate materials can also trigger a variety of masonry
problems. In particular, stiffer mortars have been seen to lead to extensive problems when
used on masonry walls, due to their excessive strength and impermeable matrix compared to
original masonry materials” (Hassapis, 2000).
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2.8.2 Grouting
“Is a term used for the introduction into a structure or into the ground of a material
in liquid form, which subsequently cures or sets into a durable solid or gel form” (Hassapis,
2000).
The evaluation of repair documents, the computational analysis of stress conditions
in repaired masonry and the knowledge obtained from interference into the substance by
experimental test, prove that there is an increase in load-bearing capacity after injection. This
is obviously caused by the reduction of cavities and faulty areas in the old masonry. Loads
can then be transferred directly and peaks of strain can be reduced.
The degree of injection depends on the specific components of the old masonry
being repaired or strengthened and on its structure and moisture content, on the composition
of the suspension as well as on the procedure selected to prepare and carry out the injection,
including the applied pressure.
In contrast to the apprehension on the part of monument preservation, it has been
discovered that hardly any new injection material intrudes into the old mortar. The grout fills
the cracks, voids and cavities, basically remains in the damaged and faulty areas of the
masonry, and does not penetrate the old mortar in the sense of a mixture. With this
exception, areas of contact between both materials are limited to the surfaces of cracks,
cavities and drill-holes resulting in more or less abrupt and plane marginal zones (Pearson,
2007).
There are various methods of grouting, the most important of which are presented
next: hand grouting, pressed injection or pumped system, vacuum system and gravity
grouting.
2.8.3 Pinning
Pinning is more repair technique than a strengthening one. The process involves the
insertion of pins into holes left by missing stones and drilled holes. During the process it is
important to replace any missing pinnings or loose stones back into their original position
and to ensure that all the replaced stones make physical contact each other. It is also used for
replacing old masonry units or for redressing the faces of old units. Small fractures and voids
can be also repaired with this method. The insertion of the pins removes the resins or grouts,
which, consequently, flow into internal cracks and fissures (Coonie, 1992).
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In doing so, this gives the wall back its full structural strength and original
appearance. Any missing pinning stones will generally be revealed by the remaining wide
joints.
2.8.4 Stitching
In general, stitching as subsequent reinforcement happens where tension or thrust
occurs which the masonry cannot withstand. Stitching is always connected with grout
injection to form the bond between steel and masonry as well as to provide corrosion
protection. In multi-leaf masonry the reinforcement bars connect the two outer leaves
through the inner filling which was strengthened by injection. As the outer leaves are usually
only one stone thick, special attention must be paid to the anchorage of the bars (Pearson,
2007).
In particular, the diameter of the drilled holes is approximately 20-40mm wide,
while the diameter of the reinforcement is usually the 12-15mm. The amount of holes drilled
per unit area is dependent on the conditions and nature of the structure, its weakness etc., but
many times there are 3-4 hoes per square meter of wall surface. The length of the holes is
usually about three times the wall´s thickness (Souden, 1990)
2.8.5 Overall strengthening of old masonry
For seismic strengthening of historic masonry buildings, the solutions usually consist
in corrections that guide us to a better behaviour against any movement in the base.
When inadequate seismic structural response is detected, actions can be directed to
different objectives: reduction in the overall weight (directed to top stories); elimination of
any asymmetric configuration in plan; continuity between the elements that transmit the
seismic forces.
2.8.6 Fibre Reinforced Polymer (FRP)
Among the innovating techniques to rehabilitate deteriorated structures, there is a
new method that has been gaining acceptation in the market due to its several advantages;
commonly know as FRP.
According to Pilakoutas (2007), some of its advantages are:
· Strength/Specify gravity (10-15 times than steel)
· Corrosion immunity
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· Fatigue characteristics
· Electromagnetic Neutrality
· Effective solution in aggressive environments
· Temperature resistance
· Low density
As a result, all this advantages makes FRR highly attractive and cost effective to be
used as a common material in strengthening works. Moreover, the use of FRP in special
applications in construction becomes cost-effective due to durability improvement, reduced
life-cycle maintenance cost and also savings from easier transportation and enhancement on
site-productivity (Triantafillou & Fardis, 1997).
Schwegler (1994) was the first person to propose and study the use of carbon
laminates as strengthening elements for masonry structures (Figure 2-16).
Table 3- 2 Modal Participating ratios for each mode.
Figure 3- 13 (a) First mode of vibration (T=0.28sec). (b) Second mode of vibration (T=0.23sec).
In the first two modes of vibration (Figures 3-13) both towers are excited in X-direction. This mode has an effective mass of 2%, confirming that is a particular vibrationmode of the towers.
The third mode (figure 3-14) acts along X-direction exciting one side of thestructure, affecting both tower and the module C. This mode has an effective participatingmass of 12%, becoming an important mode for the structure.
a) b)
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Figure 3- 14 Third mode of vibration (T=0.23sec)
Figure 3- 15 Fourth mode of vibration (T=0.22sec).
The fourth mode (Figure 3-15) is related to the excitation of the structure in Y-direction having a torsional effect on the structure. In addition a sagging effect can belocalized in the walls of the main vault. The constant lateral movement of the structure originthe development of compressive and tensile stresses in the adjacent buildings, which act asbuttresses of the main body. The differences in height between the two buildings cause anegative interaction in the walls and cupola. This mode is the most important for theresponse of the structure against seismic actions because it affects 44% of the total mass.
The following modes are less important, and basically excite the structure in atorsional mode.
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3.5.3.3 Response spectrum analysis
The seismic area under which the Church is stand was found B, corresponding to a
C=0.3g. The predominant type of soils corresponds to a very high load capacity soil formed
mostly by rocks.
The response spectrum was defined according to the Mexican code (Mexican-
Norms, 2007), which is the one used in the local area (Figure 3-16). The response spectrum
analyses were carried out in both longitudinal and transversal directions. The internal forces
were computed according to the SRSS rule and superposed with 30% in each direction in
accordance to the NTC (Mexican-Norms, 2007).
Figure 3- 16 Response Spectrum according to NTC.
The code requires that the effective mass of the considered modes to be greater than
90% of the overall mass of the structure and that every mode with an effective mass greater
than 5% must be taken into account. These requirements were satisfied by using the first 50
modes.
Damping estimation in historic masonry structures is a critical issue. Due to lack of
experimental measurements that can establish a proper damping value and moreover due to
the unique of this type of structures, a damping value of 5% was chosen for the numerical
analyses; considering the appearing of cracks and sliding in the joints. The software used for
the earthquake simulation was SAP2000®.
3.5.3.3.1 Single arch model
For the study of seismic actions, the displacement of the structure was restrained in
its perpendicular direction.
00.02520.05040.07560.1008
0.1260.15120.17640.20160.2268
0.2520.27720.30240.3276
0 0.5 1 1.5 2 2.5 3 3.5 4
Sd(g
)
T(s)
ERS type 1
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Figure 3- 17 (a)Shear stress diagram and deformed shape. (b)Stress diagram under earthquake loading inprincipal direction.
It was observed tensional stresses lower than 1kg/cm2 in most of the structure, but
surpassed in the bottom of supports and arch connections (Figure 3-17).
3.5.3.3.2 Global model
The finite element model previously discussed and shown in (Figure 3-6) and
(Figure 3-7) was presented for the study of the seismic structural behaviour of the Santo
Domingo church. All the dimensions where obtained from drawings of previous repair
works.
As concluded before, the structure of the church is clearly conceived to sustain
gravity loads. Sometimes the characteristics of the materials impede an adequate seismic
behaviour; a very heavy structure with very low carrying capacity and low ductility. In this
case a response spectra analysis is carried out to corroborate the seismic safety of the
structure.
Seismic actions are frequently variable. For earthquakes of low intensity it can be
expected that all sections present a minimum displacement, maintaining the section under
compression or perhaps with tolerable tensions. Nevertheless, in strong events, the structure
can develop high tensile stresses. In the actual condition, these tensions could origin the
collapse of the towers.
The linear response spectrum analysis of the global structure shows that the design
spectrum would produce maximum tensile stresses of around 3 kg/cm2 at the towers and
walls of module C (Figure 3-18). This clarify that with the addition of an extra section in the
Module C, the structure gained more arguments to withstand lateral forces and avoid the
collapse of one of the cupolas.
a) b)a) b)
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Figure 3- 18 (a)Principal stresses in Y-direction due to earthquake. (b)Principal stresses in X-direction dueto earthquake.
The Figure 3-19 shows in a magnified scale, the maximum displacements originated
by the design earthquake acting in X and Y directions. The maximum displacement is
presented in the top part of the towers, and it’s about 2cms in X-direction. It can be notice
that in the main structure the maximum horizontal displacement is of 0.5cms. For the
displacements along Y-direction it shows that the vaulted body displaces around 2cms, this
behaviour can lead to the detachment between the vault and its supports.
Figure 3- 19(a)Displacement contours originated by the design spectra in Y-direction. (b)Displacement contoursoriginated by the design spectra in X-direction(Contours in cms).
3.5.3.3.3 Concluding remark
Estimating that all the components will remain intact, the structural system shows a
good behaviour against its own weight and low intensity earthquakes. The forces are
transmitted axially with low stresses due to the big size of the elements. This allows masonry
a) b)
a) b)
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to resist moderate compressive and shear stresses. Otherwise, a large earthquake will cause
local damage causing arches and vaults to separate from its connection with the walls.
I would like to mention that the real structure shows a cracking in the middle span of
the vault. According to these findings it should be considered that the geometry of the vault
is suitable enough to avoid a separation between the vault and walls, but instead of this, a
plastic hinge is developed at the middle span.
As result, the computations with the response spectrum method show a good
structural behaviour of the church against low seismic events, but for the case of high
intensity earthquakes, local failures leading to local collapse in the vault are substantially to
take place and must be studied by refined methods.
3.5.3.4 Time history analysis
Time History analyses were carried out to verify the results from the response
spectrum analysis and to compute the internal forces and displacements as a function of time.
For this purpose, recordings of the 21 of October of 1995 earthquake on hard ground at a
distance of about 100 km from the epicentre and with a magnitude of Ms=6.2 were used.
The record samples the near field strong motions that triggered damage to some buildings in
the city. The duration of the recording of the motion is about 165 sec. and the maximum
accelerations are 348.61cm/s2 in the N-S direction and 441.95cm/s2 in the E-W direction
(Figure 3-20). For the computation the accelerograms are applied in two horizontal
directions as in the response spectrum analysis.
Figure 3- 20 (a) 1995 earthquake accelerograms in N-S direction (b) 1995 Earthquake accelerograms in E-W direction
3.5.3.4.1 Global model
Tensile stresses of 2kg/cm2 above the limit of the proposed material strength are
observed in the two towers (Figure 3-21). Tensile stresses are observed in the connection
between the main body and the adjacent module that can lead in the disconnection in some
areas.
a) b)
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Figure 3- 21 (a)Stresses diagram in Y-direction [95 Earthquake]. (b)Stresses diagram in X-direction [95Earthquake].
The next figure shows the development of relative low tensional stresses in the
intrados of the main arches. To reduce the detachment of units at the extrados face, the
addition of a GFRP plate is proposed to increase the tensile capacity of the structure and to
add an extra bonding between the constitutive elements.
The Figure 3-22(b) shows the stresses contours of the main facade, having
significant tensional stresses in the towers, from about 1kg/cm2.
Figure 3- 22 (a)Stresses diagram in X-direction [95 Earthquake]. (b)Maximum envelop of stresses in X-direction [95 Earthquake].
A typical mode of failure of horizontal cracking between windows due to tensile
forces clearly appears in the numerical model (Figure 3-23(a)). Maximum stresses contours
in adjacent module (Figure3-23(b)). Such stresses can lead to a large deformation in the wall
and cupola-wall connections.
a) b)
a) b)
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Figure 3- 23 (a)Stresses diagram in Y-direction [95 Earthquake]. (b)Stresses diagram in Y-direction [95Earthquake].
The Figure 3-24 shows the safety of the arches in the mezzanine and vault section.
No high tensile stresses were found to occur during the applied accelerations, it means that
the landfill above the mezzanine and the big size of the sections establish a good system
against this type of excitations. Again, this analysis was carried out without considering any
sliding in the joints.
Figure 3- 24 Maximum envelop of principal stresses in X-direction [95 Earthquake].
The time history analysis shows relative displacements in the central arches of
building-A (vaulted body); the stresses are not significant, around 0.4 kg/cm2. The local
displacement is about 0.2cms and can not lead to any sliding in the supports and activate a
typical mode of failure (Figure 3-25(a)). At difference with the response spectra, this
earthquake actives a typical torsional effect in the structure and towers, where the central
arches suffer from lateral displacements (Figure 3-25(b)). This zigzag movement can cause
an out of plane mechanisms in the top part of the longitudinal walls affecting the connection
with the vaulted roof.
a) b)
a) b)
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Figure 3- 25 (a) Maximum envelop of principal stresses in Y-direction. (b) Deformed shape under recordedaccelerations [95 Earthquake].
The maximum displacement found occurs at the arches of the vaulted body
(0.22cms) (Figure 3-26). The difference in displacements between the top and bottom part
indicates why this section of the structure presents higher concentration of tensional stresses.
Figure 3- 26 (a)Displacement contours originated by the design spectra in X-direction. (b)Displacementcontours originated by the design spectra in Y-direction(Contours in cms).
The complete results of the displacement distribution in the 4 selected joints over the
time can be found in Appendix D.
3.5.3.4.2 Concluding remark
Therefore, the results obtained by the time history analysis prove to develop similar
tensional stresses to those found with the response spectrum case, but with the only
difference that the torsional vibration mode is more obvious in the time history case.
Joint 1426
Joint 1339
Joint 1344
Joint 1365
a) b)
a) b)
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The principal stresses where slightly lower and it was found that the shear stresses
do not have a significant effect in the structure
3.5.4 Strengthening and repair recommendations
Prior to board a rehabilitation design, it is always necessary to understand whether
the building, in its existing condition, is capable of withstand the intended seismic levels.
The process used for this purpose is one of examining the deficiencies in the existing
structure to determine the principal requirements for additional strength, stiffness, or
deformation capacity.
According to the findings, the actual condition of the church is safe against gravity
loads, settlements and low intensity earthquakes. But the seismic analyses demonstrate that
one common failure mechanism in this type of structure is the tendency of the tower to
separate from its base triggering in failure at the connections between the main facade and
the vault; causing towers to continue working as isolated structures and as consequence a
collapse.
A proper solution for strengthening the towers should be the addition of
reinforcement bars in lateral and vertical directions, to function as an extra connection
between the main facade and the structure. The bars must be made of CFRP to avoid any
future affectation in the historic masonry due to material incompatibility.
For the arches a strengthening based on layers of GFRP fibres in both extrados and
extrados faces, is proposed, to give the sections more capacity to resist moments, ductility
and lateral movements.
The remedial measures were considered taking into account the modern principles of
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4 CONCLUSIONS
4.1 General conclusions and recommendations
Historical buildings and monuments are an important link between our time and
history. Unfortunately, most historical buildings have already disappeared; damaged or
collapsed because of several external factors. For this reason, it is very important to protect
them immediately, taking into account the importance of choosing the best rehabilitation
technique based on analytical and numerical assessments, so action can be taken ascertaining
that any work will lead to a better behaviour of the structure.
The thesis try to demonstrate by analytical tools and failure comparisons, how to
predict and prevent an eventual failure or collapse of the structure and corroborate that the
basic principles and criteria of structural engineering are valid for any type of construction
and that the methods applied on modern buildings, with clever modifications, can be used in
historic masonry buildings.
For the investigation of the seismic performance of the Santo Domingo church, a
three dimensional numerical model was created and analysed using an advanced earthquake
simulation software (SAP2000®). The model then was corroborated by the measurement of
its natural frequencies. The first mode period is considered a local mode of the towers
(T=0.28sec) and the third (T=0.23sec) and fourth (T=0.22 sec) modes were considered as the
fundamental modes of the structure shaking it in X and Y directions respectively. Such
modes were not expected for a heavy and medium high structure; it means that the structure
oscillate around 4.5 times per seconds. But these findings were correlated with other works
in the field (Meli, 1998) and reviewed by its deformed shapes and then by correct
interpretation of the stress concentrations taken from the numerical results.
From the static analysis was found that the structure of the church is conceived to
support gravitational loads. The geometric form of arches, cupolas and vault is enough to
distribute the forces in a good manner, allowing it to resist actions with the employed
materials. But, in contrast, individual elements as the towers in the front of the building are
flexible against lateral loads. In general is a slender structure which its relationship between
base and height induces a heavy change in the stiffness.
Two main types of analyses were carried out. A linear static response spectrum
analysis (based on (Mexican-Norms, 2007)) and a time history linear analysis (based on
accelerograms from the 21 of October of 1995 seismic event). The results of the static and
dynamic analysis cases demonstrate differences in the deformed shapes. For the response
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spectrum case the modules A & B basically moves in the Y-direction and the towers and
module C in X-direction. While for the time history analysis, the module A becomes in
torsion, a zigzag effect is developed in the middle section of the vaulted body due to the high
stiffness in Y-direction of the mezzanine and facade in relationship with this part.
These analyses provided us with very useful information related to the vibration
modes and stress diagrams. The response spectrum analysis shows stresses of around
3kg/cm2 in the towers and in one wall of the adjacent section, stresses that will lead to
cracking. The maximum displacements were found to take place in X-direction (2cms) while
for the whole structure does not surpass the 5 mm. These are considered conservative results.
For the Time history case tensional stresses are developed in the intrados of the arches of
less than 1kg/cm2. Again high tensile stresses around the walls of the adjacent section are
taking place.
Additionally it was found that general elastic behaviour of the structure is relatively
safe against gravity and minor lateral loads. This is attributed to precedent repair works, in
which the addition of buttresses and resizing of walls was correctly decided.
It is agreed the use of FRP for the strengthening works in the towers as additional
reinforcement bars and for the arches based on layers of GFRP fibres in both extrados and
extrados faces.
Recommendations for future work
As commented due to the lack of time and information, the numerical model and
parameters were not fully studied.
The previous work and strengthening recommendations only must be realized under
an extended investigation, in which is recommended:
· The most accurate determination of dimensions and material properties by
testing in situ with non-destructive methods and destructive for representative
samples, this to allow us to obtain more confidence in the results.
· The developing of analytical models that allow us to accurately describe the
nonlinear behaviour of the materials in the structure, and also to appreciate in a
better way the benefits of reinforcement.
· A dynamic testing comprising: signal acquisition, sensor choice (e.g.
accelerometers) and location (if where permanent). To calibrate the natural
frequencies and damping values of the real structure.
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· The developing of a numerical model avoiding any averaging of elements,
taking into account all nonlinear issues related to: material properties,
foundation conditions, cracking development, sliding of the joints, different
layers of the masonry walls (if exist).
· Corroboration and calibration of the FE model based on testing measurements.
· A detailed failure investigation of the building. In where all the previous repair
and strengthening works, as well as present problems, where stated and
indicated by drawings and photographs.
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References
Basilio, I., Oliveira, D. V., & Lourenco, P. B. (2004). Optimal FRP Strengthening ofMasonry Arches. 13th International brick and block masonry conference. Eindhoven:Eindhoven University of Technology.
BBC-NEWS. (2007, August 18). BBC. Retrieved August 23, 2007, from A. BBC Web site:http://news.bbc.co.uk/1/hi/world/americas/6952985.stm
Bennett, B. (2002). Lime Plaster and Render Reinforcement. The building conservationdirectory .
Berto, L., Saetta, A., Scotta, R., & Vitaliani, R. (2005, March). Failure Mechanism ofMasonry Prism Loaded in Axial Compression: Computational Aspects. Materials andStructures , 38 (2), pp. 249-256.
Binda, L., Cardani, G., & Tiraboschi, C. (2006). The Difficult Choice of Materials for theReconstruction of the Cathedral of Noto. In S. K. Kourkoulis (Ed.), Fracture and Failure ofNatural Building Stones (pp. 185-200). Netherlands: Springer.
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Appendix A
Letter of Venice
Preamble
Imbued with a message from the past, the historic monuments of generations of people
remain to the present day as living witnesses of their age-old traditions. People are becoming
more and more conscious of the unity of human values and regard ancient monuments as a
common heritage. The common responsibility to safeguard them for future generations is
recognized. It is our duty to hand them on in the full richness of their authenticity.
It is essential that the principles guiding the preservation and restoration of ancient buildings
should be agreed and be laid down on an international basis, with each country being
responsible for applying the plan within the framework of its own culture and traditions.
By defining these basic principles for the first time, the Athens Charter of 1931 contributed
towards the development of an extensive international movement which has assumed
concrete form in national documents, in the work of ICOM and UNESCO and in the
establishment by the latter of the International Centre for the Study of the Preservation and
the Restoration of Cultural Property. Increasing awareness and critical study have been
brought to bear on problems which have continually become more complex and varied; now
the time has come to examine the Charter afresh in order to make a thorough study of the
principles involved and to enlarge its scope in a new document.
Accordingly, the 2nd International Congress of Architects and Technicians of Historic
Monuments, which met in Venice from May 25th to 31st 1964, approved the following text:
Definitions
ARTICLE 1. The concept of an historic monument embraces not only the single
architectural work but also the urban or rural setting in which is found the evidence of a
particular civilization, a significant development or an historic event. This applies not only to
great works of art but also to more modest works of the past which have acquired cultural
significance with the passing of time.
ARTICLE 2. The conservation and restoration of monuments must have recourse to all
the sciences and techniques which can contribute to the study and safeguarding of the
architectural heritage.
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Aim
ARTICLE 3. The intention in conserving and restoring monuments is to safeguard them
no less as works of art than as historical evidence.
Conservation
ARTICLE 4. It is essential to the conservation of monuments that they be maintained on a
permanent basis.
ARTICLE 5. The conservation of monuments is always facilitated by making use of them
for some socially useful purpose. Such use is therefore desirable but it must not change the
lay-out or decoration of the building. It is within these limits only that modifications
demanded by a change of function should be envisaged and may be permitted.
ARTICLE 6. The conservation of a monument implies preserving a setting which is not
out of scale. Wherever the traditional setting exists, it must be kept. No new construction,
demolition or modification which would alter the relations of mass and colour must be
allowed.
ARTICLE 7. A monument is inseparable from the history to which it bears witness and
from the setting in which it occurs. The moving of all or part of a monument cannot be
allowed except where the safeguarding of that monument demands it or where it is justified
by national or international interest of paramount importance.
ARTICLE 8. Items of sculpture, painting or decoration which form an integral part of a
monument may only be removed from it if this is the sole means of ensuring their
preservation.
Restoration
ARTICLE 9. The process of restoration is a highly specialized operation. Its aim is to
preserve and reveal the aesthetic and historic value of the monument and is based on respect
for original material and authentic documents. It must stop at the point where conjecture
begins, and in this case moreover any extra work which is indispensable must be distinct
from the architectural composition and must bear a contemporary stamp. The restoration in
any case must be preceded and followed by an archaeological and historical study of
the monument.
ARTICLE 10. Where traditional techniques prove inadequate, the consolidation of a
monument can be achieved by the use of any modem technique for conservation and
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construction, the efficacy of which has been shown by scientific data and proved by
experience.
ARTICLE 11. The valid contributions of all periods to the building of a monument must
be respected, since unity of style is not the aim of a restoration. When a building includes
the superimposed work of different periods, the revealing of the underlying state can only be
justified in exceptional circumstances and when what is removed is of little interest and the
material which is brought to light is of great historical, archaeological or aesthetic value, and
its state of preservation good enough to justify the action. Evaluation of the importance of
the elements involved and the decision as to what may be destroyed cannot rest solely on the
individual in charge of the work.
ARTICLE 12. Replacements of missing parts must integrate harmoniously with the
whole, but at the same time must be distinguishable from the original so that restoration
does not falsify the artistic or historic evidence.
ARTICLE 13. Additions cannot be allowed except in so far as they do not detract from
the interesting parts of the building, its traditional setting, the balance of its composition
and its relation with its surroundings.
Historic Sites
ARTICLE 14. The sites of monuments must be the object of special care in order to
safeguard their integrity and ensure that they are cleared and presented in a seemly manner.
The work of conservation and restoration carried out in such places should be inspired by the
principles set forth in the foregoing articles.
Excavations
ARTICLE 15. Excavations should be carried out in accordance with scientific standards
and the recommendation defining international principles to be applied in the case of
archaeological excavation adopted by UNESCO in 1956. Ruins must be maintained and
measures necessary for the permanent conservation and protection of architectural features
and of objects discovered must be taken. Furthermore, every means must be taken to
facilitate the understanding of the monument and to reveal it without ever distorting its
meaning. All reconstruction work should however be ruled out "a priori." Only anastylosis,
that is to say, the reassembling of existing but dismembered parts can be permitted. The
material used for integration should always be recognizable and its use should be the least
that will ensure the conservation of a monument and the reinstatement of its form.
Publication
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ARTICLE 16. In all works of preservation, restoration or excavation, there should
always be precise documentation in the form of analytical and critical reports,
illustrated with drawings and photographs. Every stage of the work of clearing,
consolidation, rearrangement and integration, as well as technical and formal features
identified during the course of the work, should be included. This record should be placed
in the archives of a public institution and made available to research workers. It is
recommended that the report should be published.
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ICOMOS recommendations
Structures of architectural heritage, by their very nature and history (material and
assembly), present a number of challenges in conservation, diagnosis, analysis, monitoring
and strengthening that limit the application of modern legal codes and building standards.
Recommendations are desirable and necessary to ensure rational methods of analysis and
repair methods appropriate to the cultural context.
Principles
A multi-disciplinary approach is obviously required in any restoration project and
the peculiarity of heritage structures, with their complex history, requires the organisation of
studies and analysis in steps that are similar to those used in medicine. Anamnesis, diagnosis,
therapy and controls, corresponding respectively to the condition survey, identification of the
causes of damage and decay, choice of the remedial measures and control of the efficiency
of the interventions. Thus, no action should be undertaken without ascertaining the likely
benefit and harm to the architectural heritage.
Therapy should address root causes rather than symptoms. Each intervention should
be in proportion to the safety objectives, keeping intervention to the minimum necessary to
guarantee safety and durability and with the least damage to heritage values. The choice
between “traditional” and “innovative” techniques should be determined on a case-by-case
basis with preference given to those that are least invasive and most compatible with heritage
values, consistent with the need for safety and durability. At times the difficulty of
evaluating both the safety levels and the possible benefits of interventions may suggest “an
observational method”, i.e., an incremental approach, beginning with a minimum level of
intervention, with the possible adoption of subsequent supplementary or corrective measures.
The characteristics of materials used in restoration work (in particular new materials)
and their compatibility with existing materials should be fully established. This must include
long-term effects, so that undesirable side effects are avoided.
Finally, a most relevant aspect is that the value and authenticity of architectural
heritage cannot be assessed by fixed criteria because of the diversity of cultural backgrounds
and acceptable practices.
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Guidelines
A combination of both scientific and cultural knowledge and experience is
indispensable for the study of all architectural heritages. The purpose of all studies, research
and interventions is to safeguard the cultural and historical value of the building as a whole
and structural engineering is the scientific support necessary to obtain this result. The
evaluation of a building frequently requires a holistic approach considering the building as a
whole, rather than just the assessment of individual elements.
The investigation of the structure requires an interdisciplinary approach that goes
beyond simple technical considerations because historical research can discover phenomena
involving structural issues while historical questions may be answered from the process of
understanding the structural behaviour. Knowledge of the structure requires information on
its conception, on its constructional techniques, on the processes of decay and damage, on
changes that have been made and finally on its present state.
The methodology stresses the importance of an “Explanatory Report”, where all the
acquired information, the diagnosis, including the safety evaluation, and any decision to
intervene should be fully detailed. This is essential for future analysis of continuous
processes (such as decay processes or slow soil settlements), phenomena of cyclical nature
(such as variation in temperature or moisture content) and even phenomena that can
suddenly occur (such as earthquakes or hurricanes), and for future evaluation and
understanding of the remedial measures adopted in the present.
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Appendix B
a B C D E F G H
Figure B- 1 Longitudinal section A-A'
aBCDEFGH
Figure B- 2 Longitudinal section B-B'
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Figure B- 3 Transversal section C-C'
Figure B- 4 Transversal section D-D'
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Appendix C
Modal Participating Mass RatiosOutputCase StepType StepNum Period UX UY UZ SumUX SumUY SumUZ
Text Text Unitless Sec Unitless Unitless Unitless Unitless Unitless Unitless
Table C- 1 Modal participating ratios for each vibration mode.
Modal Periods And FrequenciesOutputCase StepType StepNum Period Frequency CircFreq Eigen value
Text Text Unitless Sec Cyc/sec rad/sec rad2/sec2
MODAL Mode 1 0.282433 3.5407 22.247 494.91
MODAL Mode 2 0.235932 4.2385 26.631 709.23
MODAL Mode 3 0.231895 4.3123 27.095 734.14
MODAL Mode 4 0.219753 4.5506 28.592 817.51
MODAL Mode 5 0.17981 5.5614 34.943 1221
MODAL Mode 6 0.157572 6.3463 39.875 1590
MODAL Mode 7 0.140973 7.0935 44.57 1986.5
MODAL Mode 8 0.134707 7.4235 46.643 2175.6
MODAL Mode 9 0.1339 7.4683 46.925 2201.9
MODAL Mode 10 0.128017 7.8115 49.081 2408.9
MODAL Mode 11 0.119477 8.3698 52.589 2765.6
MODAL Mode 12 0.113768 8.7898 55.228 3050.2
MODAL Mode 13 0.113242 8.8307 55.485 3078.6
MODAL Mode 14 0.109395 9.1412 57.436 3298.9
MODAL Mode 15 0.107326 9.3174 58.543 3427.3
MODAL Mode 16 0.103307 9.6799 60.821 3699.2
MODAL Mode 17 0.102862 9.7218 61.084 3731.2
MODAL Mode 18 0.098475 10.155 63.805 4071.1
MODAL Mode 19 0.096762 10.335 64.934 4216.4
MODAL Mode 20 0.095192 10.505 66.005 4356.7
MODAL Mode 21 0.092777 10.779 67.724 4586.5
MODAL Mode 22 0.089349 11.192 70.322 4945.2
MODAL Mode 23 0.088045 11.358 71.364 5092.8
MODAL Mode 24 0.085685 11.671 73.329 5377.2
MODAL Mode 25 0.083668 11.952 75.097 5639.5
MODAL Mode 26 0.081569 12.26 77.029 5933.5
MODAL Mode 27 0.077992 12.822 80.562 6490.2
MODAL Mode 28 0.073775 13.555 85.167 7253.5
MODAL Mode 29 0.073515 13.603 85.468 7304.8
MODAL Mode 30 0.071112 14.062 88.356 7806.8
MODAL Mode 31 0.06835 14.63 91.926 8450.4
MODAL Mode 32 0.067235 14.873 93.452 8733.2
MODAL Mode 33 0.062312 16.048 100.83 10167
MODAL Mode 34 0.059716 16.746 105.22 11071
MODAL Mode 35 0.058999 16.95 106.5 11342
MODAL Mode 36 0.054038 18.506 116.27 13520
MODAL Mode 37 0.050795 19.687 123.7 15301
MODAL Mode 38 0.048573 20.588 129.36 16733
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MODAL Mode 39 0.044196 22.626 142.17 20211
MODAL Mode 40 0.041969 23.827 149.71 22413
MODAL Mode 41 0.039007 25.637 161.08 25947
MODAL Mode 42 0.034282 29.17 183.28 33591
MODAL Mode 43 0.029091 34.375 215.98 46648
MODAL Mode 44 0.027612 36.216 227.55 51780
MODAL Mode 45 0.022914 43.641 274.2 75188
MODAL Mode 46 0.020045 49.887 313.45 98251
MODAL Mode 47 0.019169 52.166 327.77 107430
MODAL Mode 48 0.010953 91.303 573.67 329100
MODAL Mode 49 0.008544 117.05 735.43 540860
MODAL Mode 50 0.007364 135.8 853.26 728050
Table C- 2 Modal periods and frequencies for each vibration mode.
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Appendix D
Figure D- 1 Displacement in X-direction of joint 588 (orange) and 579 (blue) VS time.
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Figure D- 2 Displacement in X-direction of joint 591 (green) and 578 (blue) VS time.
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Figure D- 3 Displacement in Y-direction of joint 588 (orange) and 579 (blue) VS time.
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Figure D- 4 Displacement in Y-direction of joint 591 (green) and 578 (blue) VS time.
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Figure D- 5 Response spectrum curve for joint 1365 matching with the third mode of the structure at 0.23secPeriod vs. Pseudo spectral acceleration in Y-direction.
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Figure D- 6 Response spectrum curve for joint 591 matching with the first mode of the structure at 0.3secPeriod vs. Pseudo spectral acceleration in Y-direction.