ijri-cce-01-001

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


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


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


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


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


Base Shear Tabular Wind Analysis Wy

Story Load VYROOF 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 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


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

ijri-cce-01-001

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