Download Alternative Approach to Soft Storey in Seismic

SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015
Alternative Approach to Soft Storey in Seismic
Analysis of R.C.C Building Structures
AbhishekArora#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 study
finds 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,
displacement , natural time period
storey
shear,
drift
,
I. INTRODUCTION
Reinforcedconcreteframebuildings 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 than
upper 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
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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 WORK
A four - storeybuilding with R C momentresistingframe has
been chosenforthis study.
Typesofcasesusedforanalysisofstructure are as follows MODEL NO .1 Building
modelwithsoftstorey:buildingmodelwithnomasonrywallinfirst
groundstorey andfullinfillmasonry wallinall above stories with
column 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
Name
Story4
Height Elevation
mm
mm
2950
12150
Master
Story
No
None
Splice
Story
No
Similar To
Story3
2950
9200
No
None
No
Story2
2950
6250
No
None
No
Story1
3300
3300
No
None
No
0
0
No
None
No
Base
Gravity loading
Story
Story4
Story3
Story2
Story1
S.W
P.C
P.C
P.C
P.C
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LIVE
1.5
2
2
2
SIDL
2
1.5
1.5
1.5
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SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015
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 been
applied to the mass center of the building. Since the building
under consideration was in Zone–III.
Load Cases
Name
Type
Dead
Live
SIDL
EQx
EQy
FF
SPEC X
SPEC Y
Linear Static
Linear Static
Linear Static
Linear Static
Linear Static
Linear Static
Response Spectrum
Response Spectrum
Fig 2 ETABS Models
Factors and Coefficients {as per IS:1983 (P-1)-2002}
Seismic zone factor
Response reduction factor
Importance factor
Site type
Z
R
I
TYPE
0.16
4
1
II
B. Model Analysis
Model No. 1 – building with only columns at open storey
Fig3Stiffness Plot for Model with Only Columnat first floor
Fig 4Drift plot for model with only columns at first floor
Fig 1 Building Plan
TABLE 1
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SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015
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 at
open storey
Fig 6 Plan with Shear Wall
Fig 7 ETABSModel with Shear Walls
TABLE 3
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SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015
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
1.
IV. RESULTS
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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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SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015
provided at the first floor the overall stiffness in both Xdirection 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
MODEL 1(for plan having only columns)
Fig 10Sudden displacement can be easily seem in plan with column only
when earthquake occurs
MODEL 2(for plan having both column
and shear wall both)
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)
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SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015
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]
[2]
[3]
MODEL 2(for plan having both column
and shear wall both)
4. Comparison of natural time period
MODEL NO 1(for plan having only columns)
[4]
Direction
Period Used
(sec)
W
(N)
Vb
(kN)
[5]
X + Ecc. Y
0.332
30686613.31
1534330.67
[6]
Y + Ecc. X
0.294
30686613.31
1534330.67
MODEL NO 2(for plan having both column
and shear wall both)
X + Ecc. Y
Period Used
W
(sec)
(N)
0.204
30565238.41
Vb
(kN)
1528261.92
Y + Ecc. X
0.246
1528261.92
Direction
1.
2.
3.
30565238.41
[7]
[8]
[9]
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.
Sujatha A., Jiji Anna Varughese, Bindhu K.R, “The Influence of
Masonry Infill in RC Multi-Storey Buildings,” (NCTT09) 6-7 Nov
2009.
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.
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.
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.
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.
Bento R., Azevedo J., “Behavior coefficient assessment for Soft
Storey Structures”, 12WCEE,2000.
P.Agrawal, M. Shrikhande Earthquake resistant design of structure
(PHI Learning Pvt.Ltd. New Delhi, 2009).
Mario Paz & William Leigh, Structural Dynamics (Springer Pvt. Ltd.
New Delhi, 2007).
IV. CONCLUSION
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.
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 the
model with only columns is not appropriate for analysis as
compared to other model having both wall and column in the
ground storey.
The presence of wall sin upper storey makes the much
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