ANALYSIS OF SOFT STOREY FOR MULTI STORYED BUILDING IN ZONE-4

1
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, India
2 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, 2014
Review Type: peer reviewed
Volume: I, Issue : I
Citation: S.uttamraj , Research Scholar (2014) ANALY-
SIS OF SOFT STOREY FOR MULTI STRYED BUILDING
IN ZONE-4
INTRODUCTION
Soft-Storey
•A 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 storey’s due to the fact that it has
not got the walls with the same properties the other
ones have Soft storey’s 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 story’s 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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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 Building
Symmetrical 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 storey’s 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 storey’s. 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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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 structure
Building as a whole
Individual members
Failures due to soil conditions
Structural 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
storey’s 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 time’s 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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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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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
7TH STORY EQX -8765
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
12TH STORY EQY -5700
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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Base Shear Tabular Wind Analysis Wy
Story Load VY
ROOF WY -163.54
20TH STORY WY 344.25
17TH STORY WY 920.4
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 VX
ROOF SPEC-1 565.98
20TH STORY SPEC-1 1214.78
2ND STORY SPEC-1 4900.53
IST STORY SPEC-1 5038.57
BASE SPEC-1 5079.57
Base Shear In Zone-4 For Dynamic Analysis
Spec-1

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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 structures
3.IS: 875(part 1) – 1987 – Code of practice for de-
sign loads (Other than earthquake) for buildings
and structures – Dead loads.
and structures – Imposed loads
and structures – Wind loads.
6.Mark Fintel – Hand book of concrete engineering ,
second edition, CBS Publishers & Distributors-New
Delhi, 2004
7.U H Varyani – Structural Design of Multistoried
Buildings, Second edition, South Asian Publishers
– New Delhi, 2002
8.Anil K. Chopra – Dynamics of structures: Theory
and applications to Earthquake Engineering , Sec-
ond edition, Pearson Education (Singapore) Pvt. ltd
2005
9.Dr V. L. Shah &Dr S.R. Karve – Illustrated de-
sign of Reinforced concrete buildings (fifth edition) ,
Structures publications-Pune, 2005
10.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,
Hyderabad, India.
K. Mythili2
Assosiate professor, Department Of Civil Engineering,
Hyderabad, India

ANALYSIS OF SOFT STOREY FOR MULTI STORYED BUILDING IN ZONE-4

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