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1International Journal of Research and Innovation (IJRI)
International Journal of Research and Innovation (IJRI)
ANALYSIS OF SOFT STOREY FOR MULTI STORYED BUILDING IN ZONE-4
S.uttamraj1*, K. Mythili2
1 Research Scholar, Department Of Civil Engineering, Aurora's
Scientific Technological & Research Academy, Hyderabad, India2
Assistant professor , Department Of Civil Engineering, Aurora's
Scientific Technological & Research Academy, Hyderabad,
India
*Corresponding Author:
S.uttamraj , Research Scholar, Department Of Civil Engineering,
Aurora's Scientific Technological & Research Academy,
Hyderabad, India
Published: September 15, 2014Review Type: peer reviewedVolume:
I, Issue : I
Citation: S.uttamraj , Research Scholar (2014) ANALY-SIS OF SOFT
STOREY FOR MULTI STRYED BUILDING IN ZONE-4
INTRODUCTION
Soft-StoreyA soft story building is a multi-story building with
one or more floors which are soft due to struc-tural design. Soft
story buildings are characterized by having a story which has a lot
of open space such as parking garages, or large retail spaces or
floors with a lot of windows. This soft story creates a major weak
point in an earthquake, since soft stories are classically
associated with retail spaces and park-ing garages, they are often
on the lower stories of a building, and the upper floors of most
buildings are more rigid than their base floors. As a result, the
seismic behaviors of the base and the upper floors are
significantly different from each other. This phe-
nomenon is called as the soft-story irregularity. . If a
building has a floor which is 70% less stiff than the floor above
it, is considered as a soft story building. While the unobstructed
space of the soft story might be aesthetically or commercially
desir-able, it also means that there are less opportunities to
install shear walls, specialized walls which are designed to
distribute lateral forces so that a build-ing can cope with the
swaying characteristic of an earthquake.
Soft story also exists at intermediate floors too, floors which
are soft due to structural design. These floors can be especially
dangerous in earth-quakes, because they cannot cope with the
lateral forces caused by the swaying of the building during a
quake. As a result, the soft story may fail, causing what is known
as a soft story collapse.
Soft storey is the one of which the rigidity is lower than any
other storeys due to the fact that it has not got the walls with
the same properties the other ones have Soft storeys are generally
present at the entrance floor (ground floor) of the buildings. This
situation depends on the constructional purpose.
Abstract
Multi-storey buildings are becoming increasingly common in
developed and developing countries with the increase in
urbanization all over the world. Many of these buildings do not
have structural walls at ground floor level to increase the
flexibility of the space for recreational use such as parking or
for retail or commercial use. these buildings which pos-sess storey
that are significantly weaker or more flexible than adjacent storey
are known as soft storey buildings, these are characterized by
having a story which has a lot of open space. while the
unobstructed space of the soft story might be aesthetically or
commercially desirable, it also means that there are less
opportunities to install shear walls, special-ized walls which are
designed to distribute lateral forces so that a building can cope
with the swaying characteristic of an earthquake.
Soft-storey is also called as flexible storey. a large number of
buildings with soft storey have been built in recent year. but it
showed poor performance during past earthquake. soft storys are
subjected to larger lateral loads during earth-quakes and under
lateral loads their lateral deformations are greater than those of
other floors so the design of struc-tural members of soft stories
is critical and it should be different from the upper floors.
In this thesis analysis of soft-storey for high rise building in
zone 4, applying the finite element approach to analyse and explore
the behaviour of soft-storey at different floor level of building
under seismic load actions and wind load ac-tions respectively
.
ALL ANALYSIS IS CARRIED OUT BY SOFTWARE ETABS. BASE SHEAR,
STOREY DISPLACEMENT, STOREY DRIFT IS CALCULATED AND COMPARED FOR
ALL MODELS.
1401-1402
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2International Journal of Research and Innovation (IJRI)
Structural Description
The Building analyzed is a G+21 structure, 64.5 meter tall
located in 4th zone of india with a gross area of 780 square meter.
The analysis of building with soft-storey at different floor level
is carried out for seismic design and wind design resp.
Soft-Storey
INFILLED WALL OF W-230 mm (9 inch) thick wall is provided all
around the structure & with walls in-side the structure, the
inner walls are 115 mm thick plays an important role in increasing
the stiffness of building so they are considered in the
analysis.
Columns:C 900 x 900 mm of M40 grade up to 20th floor
Perspective Plan View Of G+20 Storied Building
Scope & Objective : The major aim of this unique project is
to study the load deflection behavior of soft storey buildings when
sub-jected to lateral loading and to develop a representative
seismic performance assessment procedure for soft sto-rey buildings
subject to different levels of ground shaking. Safety and minimum
damage level of a structure could be the prime requirement of high
rise buildings with soft stories to meet these requirements; the
structure should have adequate lateral strength, lateral stiffness,
and suf-ficient ductility. Among the various structural systems,
shear wall-concrete frame could be a point of choice for the
designer hence the objective of this paper is to study the effect
of soft story on structural behavior of high rise buildings and
seismic response of soft story structures with shear wall. Also
compare the soft story structural response of high rise building
with various type of shear wall arrangement on building and finding
of optimum design of earthquake resistance soft story buildings by
considering of required performance level. & one of the most
frequent reasons of the soft story behavior is the abrupt change in
the amount of the infill walls between stories. As the infill walls
are not regarded as a part of load carrying system, generally
engineers do not consider their effects on the structural behavior.
Therefore, many engineer are not conscious enough about soft story
occur-rence because of infill walls, and required attention is not
provided. In this study, effect of infill walls on structural
behavior, especially for the soft story, is investigated in order
to increase the level of knowledge and awareness.A comparative
study was performed on 3-D analysis mod-
el created in ETABS [9], a commercial computer program for the
analysis of structures.
Earthquake Effect on Soft-Storey for High Rise
BuildingSymmetrical constructions in both plan and height show a
better resistance during an earthquake than those that do not have
this symmetry. Since the presence of a soft storey which has less
rigidity than other storeys spoils the perpendicular symmetry of
the construction and if this fact was not taken into consideration,
it causes the construction to be affected by the quake. Because the
col-umns in this part are forced by the quake more than the ones in
the other parts of the building. & the walls in-crease the
rigidity at a certain degree in the construction.
There is 15 % difference of rigidity between a storey with walls
and the one without any walls. During an earth-quake more moment
and shear strength fall on the col-umns and walls in the entrance
floors than the one in the upper storeys. If the walls that exist
in other storey do not exist in the entrance floor, these columns
are forced more those in other storeys. Due to the fact that there
is less rigidity in soft storey.
To transfer lateral load from floor diaphragm to the foun-dation
suitable vertical elements are required. They may be moment
resisting frames, shear walls, bearings or a combination of these.
Shear wall is essentially a column with large depth and small
width. In general shear wall tend to be laterally much stiffer than
moment resisting frames. It is necessary to design the frame for at
least 25% of design force in case of structure having a
combi-nation of shear wall and moment resisting frame. This is
essential because if shear wall fails, there may be sudden collapse
of building.
Soft storey attracts plastic deformation resulting in the
collapse of the building. Many such failures due to soft storey
were observed for a good seismic performance it is necessary to
have high redundancy, thus even after failure of one of the member
the structure may not fail. If they are monolithically connected to
each other and if yielding takes place in one of them then
redistribution of forces takes place.
Criteria for earthquake resistant design of structure I S 1893 :
2002
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3International Journal of Research and Innovation (IJRI)
The earthquake zoning map of India divides India into 4 seismic
zones (Zone 2, 3, 4 and 5) unlike its previous version which
consisted of five or six zones for the country. According to the
present zoning map, Zone 5 expects the highest level of seismicity
whereas Zone 2 is associated with the lowest level of
seismicity.
Behavior of Buildings in past earthquakes:
Failures can be categorized as follows-Failure due to building
structureBuilding as a wholeIndividual membersFailures due to soil
conditionsStructural collapse may occur at any level and may be due
to lateral or torsional displacements, local failure of supporting
members, excessive founda-tion movement and it may also be due to
impact of very close adjoining structure which collapse during the
earthquake.
Design Consideration- for- Lateral Load Bearing Member
Lateral Load Bearing Members:
In framed buildings, horizontal forces due to wind or earthquake
are resisted by frames in proportion to their rigidities. In tall
buildings of moderate heights (say, up to 20 story), where both
frames and shear walls must be provided, horizontal forces are
as-sumed to be fully resisted by shear walls alone, with frames
being designed being designed for at least 25% of the total
horizontal load. For taller buildings, the rigidity of shear walls
in the upper storey gets reduced due to the accumulation of
deflection of the storeys below, necessitating joint participation
of frames and shear walls to resist shear walls alone, is hen no
more valid and more accurate methods must be adopted to apportion
the horizontal shear between frames and shear walls.
Problems involved in the analysis of shear wall structures
which, in essence, means to determine the share of storey shear
resisted by each sheet wall for each storey in succession. It is
assumed or that the frames, if present, do not participate in
ninety rigid in its own plane or at least it is more rigid than any
of the shear walls joining it and that the foun-dation of shear
wall is sufficiently rigid to ensure its fixity at base.
Architectural features:
A desire to create an aesthetic and functionally ef-ficient
structure drives architects to conceive won-derful and imaginative
structures. Sometimes the shape of the building catches the eye of
the visitor, sometimes the structural system of work together to
make the structure a marvel. However, each of these choices of
shapes and structure has signifi-cant bearing on the performance of
the building during past earthquake across the world is very
ed-
ucative in identifying structural configurations that are
desirable versus those which must be avoided.
Size of buildings:
In tall buildings with large height- to-base size ratio, the
horizontal movement of the floors during ground shaking is large.
In short but very long buildings, the damaging effect during
earthquake shaking are many. And, in buildings with large plan area
like warehouses, the horizontal seismic forces can be excessive to
be carried by columns and walls.
Seismic Analysis Method:
When a structure is subjected to earthquake, it re-sponds by
vibrating. An earthquake force can be resolved into three mutually
perpendicular direc-tions-the two horizontal directions (x and y)
and the vertical direction (z). This motion causes the structure to
vibrate or shake in all three directions; the predominant direction
of shaking is horizontal. All the structures are primarily designed
for grav-ity loads-force equal to mass times gravity in the
vertical direction. Because of the inherent factor of safety used
in the design specifications, most struc-tures tend to be
adequately protected against ver-tical shaking. Vertical
acceleration should also be considered in structures with large
spans, those in which stability for design, or for overall
stability analysis of structures.
Properties Of Buildings
In modeling building frame, the following material properties
and geometrical properties was used for beam, columns, masonry
infill. Normal weight concrete was chosen for finite element
analysis of building frames respectively.
Symmetry Condition s: Unsymmetrical Irregular Building.
Plan dimensions : 32mX24m.
Column Size Up to 20th Floor: 900mm X 900mm.
Beam Size :300mm X 600mm.
Beam Size ( Near Core Wall ) :750mm X 750mm.
Slab Thickness : 200mm
Typical floor Height : 3m
Plinth level Height : 1.5m
Number-Of-Floors : G+20 Upper Floor
Support Condition : Fixed
Type of Soil : Medium Type 2
Zone : IV
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4International Journal of Research and Innovation (IJRI)
S T A T I C L O A D C A S E S
STATIC CASE AUTO LAT SELF WT NOTIONAL NOTIONAL CASE TYPE LOAD
MULTIPLIER FACTOR DIRECTION
DL DEAD N/A 1.0000
LL LIVE N/A 0.0000
EQX QUAKE IS1893 2002 0.0000
EQXP QUAKE IS1893 2002 0.0000
EQXN QUAKE IS1893 2002 0.0000
EQY QUAKE IS1893 2002 0.0000
EQYP QUAKE IS1893 2002 0.0000
EQYN QUAKE IS1893 2002 0.0000
WX WIND IS875 1987 0.0000
WY WIND IS875 1987 0.0000
Displacement Graph For Soft-Storey @ Different Floors
Displacement Graph For Soft Storey @ Different Floor
Drift Graph For Soft Storey @ Different Floor
Displacement Of Soft-Storey @ Ground Floor Is Compared With
Soft-Storey @ 5 Th Floor
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5International Journal of Research and Innovation (IJRI)
Drift Of Soft-Storey @ Ground Floor Is Com-pared With
Soft-Storey @ 5 Th Floor.
Base Shear Tabular Static Analysis Eqx
Story Load VX
ROOF EQX -815
20TH STORY EQX -1896
19TH STORY EQX -2905.1
18TH STORY EQX -3769
17TH STORY EQX -5306.9
16TH STORY EQX -5931.38
15TH STORY EQX -6459.77
14TH STORY EQX -6964.14
13TH STORY EQX -7348
12TH STORY EQX -7684.68
11TH STORY EQX -7948.18
10TH STORY EQX -8213.9
9TH STORY EQX -8405.3
8TH STORY EQX -8545.3
7TH STORY EQX -8765
6TH STORY EQX -8780.48
5TH STORY EQX -8800.45
4TH STORY EQX -8831.55
3TH STORY EQX -8841.67
2ND STORY EQX -8850.34
IST STORY EQX -8861.38
BASE EQX -8861.4
Story Shear Displaying Value For Eqx For Soft Storey At Ground
Floor In Zone - 4
Base Shear Tabular Static Analysis Eqx For Zone--4
Base Shear Tabular Static Analysis EQY
Story Load VX
ROOF EQY -632.4
20TH STORY EQY -1470.57
19TH STORY EQY -2253.49
18TH STORY EQY -2961.55
17TH STORY EQY -3576.9
16TH STORY EQY -4116.8
15TH STORY EQY -4601.7
14TH STORY EQY -5029.78
13TH STORY EQY -5383.69
12TH STORY EQY -5700
11TH STORY EQY -5979.8
10TH STORY EQY -6184.87
9TH STORY EQY -6399
8TH STORY EQY -6520
7TH STORY EQY -6632
6TH STORY EQY -6725
5TH STORY EQY -6881
4TH STORY EQY -6818
3TH STORY EQY -6825
2ND STORY EQY -6835
IST STORY EQY -6855
BASE EQY -6855
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6International Journal of Research and Innovation (IJRI)
Base Shear Tabular Wind Analysis Wy
Story Load VYROOF WY -163.54
20TH STORY WY 344.25
19TH STORY WY 533.74
18TH STORY WY 714.73
17TH STORY WY 920.4
16TH STORY WY 1101.31
15TH STORY WY 1265
14TH STORY WY 1430
12TH STORY WY 1594
11TH STORY WY 1751
10TH STORY WY 1907
9TH STORY WY 2047
8TH STORY WY 2187
7TH STORY WY 2294
6TH STORY WY 2401
5TH STORY WY 2508
4TH STORY WY 2698
3TH STORY WY 2796
2ND STORY WY 2889
IST STORY WY 2997
GRNDLVL WY 2996.99
Base Shear In Zone-4 For Wind Analysis Wx
Base Shear Tabular Dynamics Analysis Spec1-For Zone-4
Story Load VXROOF SPEC-1 565.98
20TH STORY SPEC-1 1214.7819TH STORY SPEC-1 1739.3418TH STORY
SPEC-1 2125.8617TH STORY SPEC-1 2415.7516TH STORY SPEC-1
2636.4115TH STORY SPEC-1 2861.6714TH STORY SPEC-1 2981.7313TH STORY
SPEC-1 3105.9712TH STORY SPEC-1 3230.9711TH STORY SPEC-1
3230.1210TH STORY SPEC-1 3368.259TH STORY SPEC-1 3520.108TH STORY
SPEC-1 3699.557TH STORY SPEC-1 3906.626TH STORY SPEC-1 4113.695TH
STORY SPEC-1 4320.754TH STORY SPEC-1 4541.423TH STORY SPEC-1
4734.882ND STORY SPEC-1 4900.53IST STORY SPEC-1 5038.57
BASE SPEC-1 5079.57
Base Shear In Zone-4 For Dynamic Analysis Spec-1
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7International Journal of Research and Innovation (IJRI)
Discussion Of Results
Using Etabs-9.6 Software The Soft-Storey For High Rise Building
In Zone-4 Is Analyzed For Different Floor Levels I.E. (Soft-Storey
@ Ground Floor, @ 5th Floor, @ 10th Floor & 15th Floor). From
The Very Limited Study Done An Attempt Has Been Made To Draw The
Following General & Specific Conclusion.
The result of the present study shows that soft-sto-rey floor
will have very determinant effect on struc-tural behavior of
building and structural capacity under lateral loads. Displacement
and relative story drifts are affected by the structural
irregularities.
Scope For Further Study
The present study is confirmed to anlysis of soft-storey for
high rise building in zone-4 for different floor levels, the study
may however be extended to soft-storey with openings at different
location & with percentage of shear walls.
Conclusion
The Soft-Storey For High Rise Building In Zone-4 Is Analyzed For
Different Floor Levels I.E. (Soft-Storey @ Ground Floor, @ 5th
Floor, @ 10th Floor & 15th Floor). From The Very Lim-ited Study
Done An Attempt Has Been Made To Draw The Following General &
Specific Conclu-sion.
The result of the present study shows that soft-storey floor
will have very determinant effect on structural behavior of
building and structural capacity under lateral loads. Displacement
and relative story drifts are affected by the structural
irregularities.
Displacement: The displacement in the struc-ture due to seismic
effect for soft storey at differ-ent floor is tabulated below.
Check any displace-ment (especially wind load) by H/500.
Storey drift: The drift in the structure due to seismic effect
for soft storey at different floor is. As per Indian standard,
Criteria for earthquake resistant design of structures, IS 1893
(Part 1): 2002, the storey drift in any storey due to ser-vice load
shall not exceed 0.004 times the storey height.
shear wall W/O 5% 10% 15%
STOREY ROOF ROOF ROOF ROOF
Displacements in x
0.007728 0.013457 0.008601 0.007190
Increase values in %
4.74% 11.28% 13%
Displacements in y
0.00170 0.02498 0.00092 0.020320
Increase values in %
13% 45% 10.95%
References
1.IS: 456 2000 Code of practice for plain and Reinforced
concrete.2.IS 1893(part 1) 2002 : Criteria for Earthquake resistant
Design of structures3.IS: 875(part 1) 1987 Code of practice for
de-sign loads (Other than earthquake) for buildings and structures
Dead loads.4.IS: 875(part 2) 1987 Code of practice for de-sign
loads (Other than earthquake) for buildings and structures Imposed
loads5.IS: 875(part 3) 1987 Code of practice for de-sign loads
(Other than earthquake) for buildings and structures Wind
loads.6.Mark Fintel Hand book of concrete engineering , second
edition, CBS Publishers & Distributors-New Delhi, 20047.U H
Varyani Structural Design of Multistoried Buildings, Second
edition, South Asian Publishers New Delhi, 20028.Anil K. Chopra
Dynamics of structures: Theory and applications to Earthquake
Engineering , Sec-ond edition, Pearson Education (Singapore) Pvt.
ltd 20059.Dr V. L. Shah &Dr S.R. Karve Illustrated de-sign of
Reinforced concrete buildings (fifth edition) , Structures
publications-Pune, 200510.C.V.R Murthy Earthquake Tips, Indian
Insti-tute of Technology Kanpur , Sponsored by Building Materials
and Technology Promotion Council, New Delhi, 2004
Author
S.uttamraj1*, Research Scholar, Department Of Civil Engineering,
Aurora's Scientific Technological & Research Academy,
Hyderabad, India.
K. Mythili2Assosiate professor, Department Of Civil Engineering,
Aurora's Scientific Technological & Research Academy,
Hyderabad, India
Abstract