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SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015

ISSN: 2348 – 8352 www.internationaljournalssrg.org Page 40

Alternative Approach to Soft Storey in Seismic

Analysis of R.C.C Building StructuresAbhishekArora#1

# PG Scholar, Department of Civil Engineering, SDDIET, (Kurukshetra University), Haryana, India

Abstract- With urbanization and increasing unbalance of

required area to availability, it is important to provide open

ground storey in both type of buildings that is commercial

and residential. These open storey’s without brick infill reduce

the stiffnessof theload carrying memberand progressive increase

in load exhibit higher stresses in the load carrying member and

these members i.e. columns fail as the plastic hinges are not for

medon predefined positions. Therefore, the collapse of this soft

storey during earthquake has caused structural engineer store

think the design of a soft storey. The present analytical studyfinds out some provisions to soft storey which can reduce the

damage during earthquake. The modeling of the whole building

is carried out using the computer program ETABS. In this study

deals with provision to soft storey in seismic analysis of RCC

building has been given in two ways, firstly by providing stiff

column which increases the stiffness of the load carrying

member or byprovidingadjacent infillwall panelin buildingframe

which increase the load carrying strength.

Keywords- stiffness, shear wall, storey shear, drift ,

displacement , natural time period

I. INTRODUCTIONReinforcedconcreteframebuildings are becoming progressively

common in India. Many RCC buildings constructed in having

a feature open the ground level storey for the purpose of

parking, i.e. partition walls are not provided in between the

columns inthe ground storey

The two distinct characteristic of the building having stilt

parking are as follows -

Difference in flexibility, i.e. the relative horizontal

displacement in the ground storey is much larger than

upper story having both columns as well aswall.

Thisflexiblegroundstoreyis also called softstorey.

Ground storey having only columns are weaker thanupper storey having both column and walls i.e. the

lower storey can bear the horizontal earthquake force

less efficiently than the upper storey.

II. APPROCH TOSOFTSTOREY

A . By Providing Stiff Column at Open Ground Storey

Stiffness of column is directly proportional to its load carrying

capacity i.e. higher the stiffness, higher is the load carrying

capacity. Stiffness can be increased by increasing the size of these

loads carrying member as they are able to bear the excessive load

during earthquake.

B.

By Providing Brick Infill with Column at Open storey

Masonry in fill has several advantages like good sound and heat

insulation properties, high lateral strength and stiffness. This

increases strength and stiffness of RC frame and hence to

decrease lateral drift, energy dissipation capacity due to cracking

of infill and friction between in fill and frame

III. ANALYTICAL WORKA four - storeybuilding with RCmomentresistingframe has been chosenforthis study.Typesofcasesusedforanalysisofstructure are as follows -

MODEL NO .1 -Buildingmodelwithsoftstorey:buildingmodelwithnomasonrywallinfirstgroundstorey andfullinfillmasonry wallinall above stories withcolumn size 300 mm x 600 mm

MODEL NO .2 -Building modelwith column and masonry wall in the ground storey

and one full in fill masonry wall in all above stories.

A.

StructuralData

Story Data

NameHeight

mm

Elevation

mm

Master

StorySimilar To

Splice

Story

Story4 2950 12150 No None No




Base 0 0 No None No

Gravity loading

Story S.W LIVE SIDL

Story4 P.C 1.5 2

Story3 P.C 2 1.5

Story2 P.C 2 1.5

Story1 P.C 2 1.5

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P.C- PROGRAM CALCULATED

SIDL- SUPER IMPOSED DEAD LOAD

Lateralloading(as perIS: 1893(Part-I)-2002)

Lateral loading consists of earthquake loading. Earthquake

loading has been calculated by the program and it has beenapplied to the mass center of the building. Since the building

under consideration was in Zone – III.

Load Cases

Name Type

Dead Linear Static

Live Linear Static

SIDL Linear Static

EQx Linear Static

EQy Linear Static

FF Linear Static

SPEC X Response Spectrum

SPEC Y Response Spectrum

Factors and Coefficients {as per IS:1983 (P-1)-2002}

Seismic zone factor Z 0.16

Response reduction factor R 4

Importance factor I 1

Site type TYPE II

B.

Model Analysis

Model No. 1 – building with only columns at open storey

Fig 1 Building Plan

Fig 2 ETABS Models

Fig3Stiffness Plot for Model with Only Columnat first floor

Fig 4Drift plot for model with only columns at first floor

TABLE 1


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STOREY DRIFT AND STIFFNESS FOR PLAN HAVING ONLY COLUMNS

TABLE 2

CHECK FOR SOFT STOREY (FOR PLAN HAVING ONLY COLUMNS)

Model No. 2 – Building with both shear wall and column atopen storey

Fig 6 Plan with Shear Wall Fig 7 ETABSModel with Shear Walls

TABLE 3


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STOREY DRIFT AND STIFFNESS FOR PLAN HAVING COLUMNS&SHEAR WALL BOTH

TABLE 4

CHECK FOR SOFT STOREY (FOR PLAN HAVING BOTH COLUMN AND SHEAR WALL BOTH)

Fig 8 - Stiffness Plot for Model with Shear Wall at First Floor Fig 9 Drift Plot for Model with Shear Wall and columns at First Floor

IV. RESULTS

1.

In Model No. 1, which contains columns at the first

storeyhas less stiffness as compared to the Model No. 2

having shear wall at the first wall. When shear wall is


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provided at the first floor the overall stiffness in both X-

direction and Y-direction is increased due to which the

load carrying capability for this floor will be also

increased, which will act more predominantly when

earthquake occurs.

2.

The comparison for story displacement can be done

Fig 10Sudden displacement can be easily seem in plan with column only

when earthquake occurs

Fig 11Even displacement can be easily seem in plan with shear wall and

column when earthquake occurs

3.

Comparison with lateral load acting

MODEL 1(for plan having only columns)

MODEL 2(for plan having both column

and shear wall both)

`

MODEL 1(for plan having only columns)


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MODEL 2(for plan having both column


4. Comparison of natural time period

MODEL NO 1(for plan having only columns)

DirectionPeriod Used

(sec)

W

(N)

V b

(kN)

X + Ecc. Y 0.332 30686613.31 1534330.67

Y + Ecc. X 0.294 30686613.31 1534330.67

MODEL NO 2(for plan having both column


IV. CONCLUSION

1. WhenModel No. 1issubjectedtolateral load,each floorwill

drift with respect to adjacent floors as each floor mass

actsindependently. Thus the distribution of horizontal

shear will be distributed across floors as building frame

act in flexible manner. In presence of infill wall and

column as in Model No. 2, mass of the upper floors to act

together as a single mass, as relative drift between

adjacent floors is restricted.

2.

Natural time period for the model having on column in the

ground storey is more than the model having both column and

shear wall in the ground storey. Thus this indicates that themodel with only columns is not appropriate for analysis as

compared to other model having both wall and column in the

ground storey.

3. The presence of wall sin upper storey makes the much

stiffer than open ground storey. Hence the upper storey

move almost together as a single block and most of the

horizontal displacement of the building occurs in the soft

ground storey itself such building moves to and fro when

earthquake occurs.

Thus it is clear that building with only column in the ground

storey has poor performance during earthquake as compared to

building with both wall and column in the ground storey.

REFERENCES[1]

J. N. Arlekar, S. K. Jain and C.V.R. Murty, “Seismic Response of RC

Frame Buildings with Soft First Storeys,” Dept. of Civil Engineering,

IIT Kanpur, India. (CBRI) 1997.[2]

Sujatha A., Jiji Anna Varughese, Bindhu K.R, “The Influence of

Masonry Infill in RC Multi-Storey Buildings,” (NCTT09) 6-7 Nov

2009.

[3]

S. Haque, Khan M. A., “Seismic Vulnerability of Columns of RC

Framed Buildings with Soft Ground Floor,” International Journal Of

Mathematical Models And Methods In Applied Sciences, Issue3,Volume-2,2008.

[4]

M.R. Amin, P. Hasan, B.K.M.A. Islam, “Effect of soft storey on

multistoried reinforced concrete building frame,” Bangladesh, ISBN:9789843343635, 4th Annual Paper Meet and 1stCivil Engineering

Congress, December 22-24, 2011.

[5]

C V R Murty, the Classroom section, a series of short articles,'Earthquake Tips', related to earthquakes design & construction of

buildings. IIT Kanpur and BMTPC, New Delhi. August 2004.[6]

A.K. Chopra, D.P. Clough, R.W. Clough, “Earthquake Resistance of

Building with a „SOFT‟ First Storey”, Earthquake Engineering and

Structural Dynamics, Vol.1, 347-355, 1973.

[7] Bento R., Azevedo J., “Behavior coefficient assessment for Soft

Storey Structures”, 12WCEE,2000.

[8]

P.Agrawal, M. Shrikhande Earthquake resistant design of structure(PHI Learning Pvt.Ltd. New Delhi, 2009).

[9]

Mario Paz & William Leigh, Structural Dynamics (Springer Pvt. Ltd.

New Delhi, 2007).DirectionPeriod Used

(sec)

W

(N)

V b

(kN)

X + Ecc. Y 0.204 30565238.41 1528261.92

Y + Ecc. X 0.246 30565238.41 1528261.92

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