International Journal of Research and Innovation (IJRI)
International Journal of Research and Innovation (IJRI) 1401-1402
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
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 possess 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, specialized 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 earthquakes and under lateral loads their lateral deformations are greater than those of other floors so the design of structural 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 actions respectively . ALL ANALYSIS IS CARRIED OUT BY SOFTWARE ETABS. BASE SHEAR, STOREY DISPLACEMENT, STOREY DRIFT IS CALCULATED AND COMPARED FOR ALL MODELS.
*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) ANALYSIS 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 structural 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 parking 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 desirable, it also means that there are less opportunities to install shear walls, specialized walls which are designed to distribute lateral forces so that a building 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 earthquakes, 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.
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International 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 inside 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
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 columns in this part are forced by the quake more than the ones in the other parts of the building. & the walls increase 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 earthquake more moment and shear strength fall on the columns 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 foundation 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 combination of shear wall and moment resisting frame. This is essential because if shear wall fails, there may be sudden collapse of building.
Scope & Objective : The major aim of this unique project is to study the load deflection behavior of soft storey buildings when subjected to lateral loading and to develop a representative seismic performance assessment procedure for soft storey 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 sufficient 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 occurrence 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-
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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International 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 followsFailure 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 foundation 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 assumed 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.
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 responds by vibrating. An earthquake force can be resolved into three mutually perpendicular directions-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 gravity 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 structures tend to be adequately protected against vertical 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 Irregular Building.
s: Unsymmetrical
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 foundation of shear wall is sufficiently rigid to ensure its fixity at base.
•Plan dimensions
: 32mX24m.
•Slab Thickness
: 200mm
Architectural features:
•Typical floor Height
: 3m
A desire to create an aesthetic and functionally efficient structure drives architects to conceive wonderful 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 significant bearing on the performance of the building during past earthquake across the world is very ed-
•Plinth level Height
: 1.5m
•Column Size Up to 20th Floor: 900mm X 900mm. •Beam Size
:300mm X 600mm.
•Beam Size ( Near Core Wall ) :750mm X 750mm.
•Number-Of-Floors
: G+20 Upper Floor
•Support Condition •Type of Soil •
: Fixed
: Medium Type 2
Zone
: IV 3
International Journal of Research and Innovation (IJRI) STATIC LOAD CASES STATIC CASE
CASE TYPE
DL
DEAD
LL
LIVE
AUTO LAT LOAD N/A
N/A
SELF WT MULTIPLIER
NOTIONAL NOTIONAL FACTOR DIRECTION
Displacement Graph For Soft Storey @ Different Floor
1.0000 0.0000
EQX
QUAKE
EQXP
QUAKE
IS1893 2002 IS1893 2002
EQXN
QUAKE
IS1893 2002
EQY
QUAKE
IS1893 2002
EQYP
QUAKE
IS1893 2002
EQYN
QUAKE
IS1893 2002
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
WX
WIND
IS875 1987
0.0000
WY
WIND
IS875 1987
0.0000
Displacement Graph For Soft-Storey @ Different Floors
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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International Journal of Research and Innovation (IJRI)
Drift Of Soft-Storey @ Ground Floor Is Compared With Soft-Storey @ 5 Th Floor.
Base Shear Tabular Static Analysis Eqx For Zone--4
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
2ND STORY
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
-8841.67
5TH STORY
EQY
-6881
EQX
-8850.34
4TH STORY
EQY
-6818
IST STORY
EQX
-8861.38
3TH STORY
EQY
-6825
BASE
EQX
-8861.4
2ND STORY
EQY
-6835
IST STORY
EQY
-6855
BASE
EQY
-6855
Story Shear Displaying Value For Eqx For Soft Storey At Ground Floor In Zone - 4
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International Journal of Research and Innovation (IJRI)
Base Shear Tabular Wind Analysis Wy Story
Load
VY
ROOF
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
4TH STORY
Base Shear Tabular Dynamics Analysis Spec1For Zone-4 Story
Load
VX
ROOF
SPEC-1
565.98
20TH STORY
SPEC-1
1214.78
19TH STORY
SPEC-1
1739.34
18TH STORY
SPEC-1
2125.86
17TH STORY
SPEC-1
2415.75
16TH STORY
SPEC-1
2636.41
15TH STORY
SPEC-1
2861.67
14TH STORY
SPEC-1
2981.73
13TH STORY
SPEC-1
3105.97
12TH STORY
SPEC-1
3230.97
11TH STORY
SPEC-1
3230.12
10TH STORY
SPEC-1
3368.25
9TH STORY
SPEC-1
3520.10
8TH STORY
SPEC-1
3699.55
7TH STORY
SPEC-1
3906.62
2508
6TH STORY
SPEC-1
4113.69
WY
2698
5TH STORY
SPEC-1
4320.75
3TH STORY
WY
2796
4TH STORY
SPEC-1
4541.42
2ND STORY
WY
2889
3TH STORY
SPEC-1
4734.88
2ND STORY
SPEC-1
4900.53
IST STORY
SPEC-1
5038.57
BASE
SPEC-1
5079.57
IST STORY
WY
2997
GRNDLVL
WY
2996.99
Base Shear In Zone-4 For Wind Analysis Wx
Base Shear In Zone-4 For Dynamic Analysis Spec-1
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International Journal of Research and Innovation (IJRI)
Discussion Of Results
References
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.
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 design loads (Other than earthquake) for buildings and structures – Dead loads. 4.IS: 875(part 2) – 1987 – Code of practice for design loads (Other than earthquake) for buildings and structures – Imposed loads 5.IS: 875(part 3) – 1987 – Code of practice for design 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, 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 , Second edition, Pearson Education (Singapore) Pvt. ltd 2005 9.Dr V. L. Shah &Dr S.R. Karve – Illustrated design of Reinforced concrete buildings (fifth edition) , Structures publications-Pune, 2005 10.C.V.R Murthy – Earthquake Tips, Indian Institute of Technology Kanpur , Sponsored by Building Materials and Technology Promotion Council, New Delhi, 2004
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. Scope For Further Study The present study is confirmed to anlysis of softstorey 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 Zone4 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 softstorey 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 structure due to seismic effect for soft storey at different floor is tabulated below. Check any displacement (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 service 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
4.74%
11.28%
13%
Increase values in % Displacements in y
Increase values in %
0.00170
0.02498
0.00092
0.020320
13%
45%
10.95%
Author
S.uttamraj1*, Research Scholar, Department Of Civil Engineering, Aurora's Scientific Technological & Research Academy, Hyderabad, India.
K. Mythili2 Assosiate professor, Department Of Civil Engineering, Aurora's Scientific Technological & Research Academy, Hyderabad, India
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