International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
Performance Based Seismic Evaluation of G+6 RC
Buildings Considering Soil Structure Interaction
Ramesh Baragani#1, Dr.S.S.Dyavanal*2
#1
P.G. Student, Civil Engineering Department, BVBCET, Hubli, Karnataka, India
Professor, Civil Engineering Department, BVBCET, Hubli, Karnataka, India
*2
Abstract— Though the structures are supported on soil, most of
the structural designers do not consider the soil structure
interaction effect during an earthquake. Different soil properties
can affect seismic waves as they pass through a soil layer. When
a structure is subjected to an earthquake excitation, it interacts
with the foundation and soil, and thus changes the motion of the
ground. It means that the shaking of the whole ground structure
system is influenced by type of soil as well as by the type of
structure. Buildings are supposed to be of engineered
construction in sense that they might have been analyzed and
designed to meet the provision of relevant codes of practice. The
prime importance of this paper is to investigate the effects of soilstructure interaction on seven storey RC buildings with various
soil types. Further to study the differences in the results of
pushover analysis due to default and user-defined hinge
properties. Non-linear static pushover analysis as per the
provisions mentioned in FEMA 440 are assumed. Momentcurvature relationships are developed as per the IS 456 : 2000.
The non-linear response of building frames namely; performance
point, location of hinges, ductility ratio, safety ratio and global
stiffness are compared among the models. Authors conclude that
safety ratio varies inversely with the stiffness of soil. Most of
flexural hinges are found within the life safety range at the
ultimate state. The observations clearly indicate that the userdefined hinge model is superior than the default-hinge model in
reflecting nonlinear behaviour of the structure.
precisely under the influence of seismic motion [2]. Present
design practice for dynamic loading assumes the building to
be fixed at their bases. Whereas, in reality supporting soil
medium allows movement to some extent due to their natural
ability to deform which decrease the overall lateral stiffness of
the structural system resulting in the lengthening of lateral
natural periods.
II.
DESCRIPTION OF STRUCTURES
In this paper the study has been carried out for seven
storeyed 2D RC frame building models with varying soil
conditions. The buildings are located in seismic zone III. The
bottom storey height is 4.8 m and upper floors height is taken
as 3.6 m for all buildings [3]. The buildings are kept
symmetric to avoid torsional response under pure lateral
forces.
In the seismic weight calculations, only 25% of the live
load is considered [4]. The building is modeled to represent all
existing components that influence the mass, strength,
stiffness, and deformability of the structure. Slabs loads are
applied on the beam. Masonry brick are modeled by
considering equivalent diagonal strut. The material properties
and thickness of struts are same as that of masonry wall and
the effective width of strut is calculated as proposed by Smith
Keywords— Soil Structure Interaction, Pushover Analysis, and Hendry [5], M (moment), PM (axial force and moment),
Default Hinge, User Defined Hinge, Performance Levels, V (Shear) and P (axial force) user defined hinge properties as
Ductility Ratio, Safety Ratio, Global Stiffness.
per FEMA 356 [6] are assigned at rigid ends of beam, column,
and strut elements respectively.
I.
INTRODUCTION
The building models considered for the study are
supported on
Several studies have been made on the effect of soil1. Hard soil and has no walls in the first storey and
structure interaction problems to obtain more realistic analysis.
brick masonry wall in the upper storeys and building
They have quantified the effect of interaction behaviour and
is modeled as bare frame. However the masses of
established that there is redistribution of forces in the structure
walls are included.
and soil mass. Hence, structures and their supporting soils
2. Medium soil and has no walls in the first storey and
should be considered as a single compatible unit. The
brick masonry wall in the upper storeys and building
interaction effects are found quite significant, particularly for
is modeled as bare frame. However the masses of
the structures resting on highly compressible soils. The
walls are included.
flexibility of soil mass causes the differential settlement and
3. Soft soil and has no walls in the first storey and brick
rotation of footings under the application of load. The relative
masonry wall in the upper storeys and building is
stiffness of structure, foundation and soil influence the
modeled as bare frame. However the masses of walls
interaction behaviour of structure-foundation-soil system [1].
are included.
The process in which, the response of the soil influences the
4.
Hard soil and has no walls in the first storey and
motion of the structure and vice versa, is referred to as Soilbrick masonry wall in the upper storeys. However
Structure Interaction (SSI). Implementing soil-structure
stiffness and mass of walls are included and building
interaction effects enables the designer to assess real
is modeled as soft storey.
displacements of the soil-foundation structure system
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International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
5.
6.
Medium soil and has no walls in the first storey and
brick masonry wall in the upper storeys. However
stiffness and mass of walls are included and building
is modeled as soft storey.
Soft soil and has no walls in the first storey and brick
masonry wall in the upper storeys. However stiffness
and mass of walls are included and building is
modeled as soft storey.
The material and soil properties considered in the present
paper are specified in Table I and II respectively. The load
combinations for equivalent static and response spectrum
analysis are considered as 1.2 (DL+LL+EQX) and 1.2
(DL+LL+RSX) respectively [4]. The plan and elevation of the
buildings considered are shown in Fig. 1, Fig. 2, and Fig. 3
Fig. 3 Elevation of seven storeyed brick infill buildings with spring supports
TABLE I
MATERIAL CONSIDERED IN THE STUDY [7]
Material Properties
Values
Grade of concrete, Fck
25 Mpa
Grade of steel, Fy
415 Mpa
Modulus of Elasticity of brick wall
3285.9 Mpa
Modulus of Elasticity of steel, Es
20,0000 Mpa
TABLE II
SOIL PROPERTIES [3]
Fig..1 Plan of the building
Shear
modulus
Type of
soil
S.B.C of
soil
(kN/m2)
Young’s
modulus
(kN/m2)
Poisson’s
ratio
Soft
120
15000
0.45
5172.41
Medium
160
50000
0.45
17241.37
Hard
250
200000
0.45
68965.51
(kN/m2)
It is highly uneconomical to demolish and reconstruct
them as per seismic code provisions. It is a wiser to retrofit
and strengthen them after evaluating their strength and
performance. Therefore, it is necessary to use non linear
analysis to evaluate the performance of existing buildings.
Non linear static pushover analysis is carried out with user
defined hinges.
Fig. 2. Elevation of seven storeyed brick infill buildings with spring supports
III.
METHODOLOGY
The majority of the existing RC multistorey buildings in
our country are still under threat, because buildings are not
designed as per seismic codes, faulty construction practices
and lack of knowledge for earthquake resistant design.
ISSN: 2231-5381
A. User defined hinges
Moment-curvature relationships are predicted in order to
define the user-defined plastic hinge properties. The moment
curvature relationships are developed as per IS: 456 – 2000[8].
The definition of user-defined hinge properties requires
moment–curvature analysis of each element. For the problem
defined, building deformation is assumed to take place only
due to moment under the action of laterally applied
earthquake loads. Thus user-defined M3 hinges were assigned
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International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
at rigid ends where flexural yielding is assumed to occur.
Moment-curvature relationships are developed for beams,
columns in SAP2000 to represent the flexural characteristics
of plastic hinges at the ends
[6] The ultimate strain in the concrete for the column is
calculated as 0.0035-0.75 times the strain at the least
compressed edge (IS 456 : 2000) [8].
1) Moment Curvature for Beam Section
Following procedure is adopted for the determination of
moment-curvature relationship considering unconfined
concrete model as given in stress-strain block shown in the
Fig as per IS 456 : 2000 [8]. The stress-strain block for beam
is shown in Fig. 4.
z
Fig. 5 Moment Curvature curve for beam
2) Moment Curvature for Column Section
Following procedure is adopted for the determination of
moment-curvature relationship for column.
1. Calculate the maximum neutral axis depth xumax from
the equation 3.
Fig. 4 Stress-Strain block for beam [9]
1.
2.
3.
4.
5.
6.
7.
Calculate the neutral axis depth by equating
compressive and tensile forces.
Calculate the maximum neutral axis depth (xumax)
from the relation 1.
 fy


 0.002 
0.0035  E s


xu
( d  xu ) …………………….. (1)
Divide the xumax in to equal laminae.
For each value of xu get the strain in fibers.
Calculate the compressive force in fibers
corresponding to neutral axis depth.
Then calculate the moment from compressive force
and lever arm (C×Z).
Now calculate the curvature by the relation 2.
s
 
d  x u …………………………………(2)
8.
Plot moment curvature curve. The curve is shown in
Fig. 5.
Assumption made in obtaining Moment Curvature Curve
for beam and column
[1] The strain is linear across the depth of the section
(‘Plane sections remain plane’).
[2] The tensile strength of the concrete is ignored.
[3] The concrete spalls off at a strain of 0.0035 86].
[4] The point ‘D’ is usually limited to 20% of the yield
strength, and ultimate curvature,u with that [10].
[5] The point ‘E’ defines the maximum deformation
capacity and is taken as 15y whichever is greater
[10].
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0 . 0035
xu
2.
3.
4.
5.
6.
7.



…………………….. (3)
N.A depth is calculated by assuming the neutral axis
lies within the section.
The value of xu is varied (trial and error) until the
value of load (P) tends to zero. At P = 0 kN the value
of xu obtained is the initial depth of N.A.
Similarly N.A depth is varied until the value of
moment (m) tends to zero. At M = 0 kN-m the value
of xu obtained will be the final depth of N.A.
The P-M interaction Curve as shown Fig. 6. is
plotted for the obtained value of load (P) and
Moment (M).
For the different values of xu the strain in concrete is
calculated by using the similar triangle rule.
The curvature values are calculated using relation 4,

8.
 fy

 0 . 002
E
  s
(d  xu )
c
xu ……………………………………. (4)
Plot the moment curvature curve as shown in Fig. 7.
Fig. 6 P M Interaction Curve
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International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
load carrying capacity of the structure. The initial stiffness
of the structure is obtained from the tangent at pushover
curve at the load level of 10% that of the ultimate load and the
maximum roof displacement of the structure is taken that
deflection beyond which the collapse of structure takes
place [6].
IV.
A.
Fig. 7 Moment Curvature relations for Column
B. Pushover analysis
Pushover analysis is a static non-linear procedure in
which the magnitude of the lateral load is incrementally
increased maintaining a predefined distribution pattern
along the height of the building. With the increase in the
magnitude of loads, weak links and failure modes of the
building can be found. Pushover analysis can determine the
behaviour of a building, including the ultimate load and
the maximum inelastic deflection. At each step, the base
shear and the roof displacement can be plotted to
generate the pushover curve for the structure. Pushover
analysis as per FEMA 440 [11] guide lines is adopted. The
models are pushed in a monotonically increasing order in a
particular direction till the collapse of the structure. 4%
of height of building [10] as maximum displacement is
taken at roof level and the same is defined in to several
steps. The global response of structure at each
displacement level is obtained in terms of the base shear,
which is presented by pushover curve. The peak of this
curve represents the maximum base shear i.e., maximum
RESULTS AND DISCUSSIONS
A. Performance evaluation of building models
Performance based seismic evaluation of building models are
carried out by non linear static pushover analysis (i.e.
Equivalent static pushover analysis and Response spectrum
pushover analysis). User defined hinges are assigned for
building models along the longitudinal direction.
1) Performance point and location of hinges
The base force, displacement, and the location of the hinges
at the performance point, for various performance levels along
longitudinal direction for all building models are presented in
the Table III to VI. In most of the buildings, flexural plastic
hinges are formed in the first storey because of open ground
storey. The plastic hinges are formed in the beams and
columns.
TABLE III
PERFORMANCE POINT AND LOCATION OF HINGES FOR BARE FRAME BUILDINGS WITH DEFAULT HINGES
Equivalent Static Method
Soil type
Hard
Medium
Soft
No of
stoteys
Performance Point
Location of hinges
Base shear (kN)
Displacement (mm)
A-B
B-IO
Yield
1153.77
150.11
221
3
IOLS
0
LS-CP
CP to E
0
0
TOTA
L
224
Ultimate
1904.64
317.84
208
12
1
0
3
224
Yield
923.019
115.47
221
3
0
0
0
224
Ultimate
1360.46
257.571
208
12
1
0
3
224
Yield
514.274
88.697
202
22
0
0
0
224
Ultimate
732.581
350.248
167
31
0
23
3
224
LSCP
1
CP
to E
0
TO
TAL
224
2
8
Response Spectrum Method
Soil type
Hard
No of
stoteys
Yield
Ultimate
Performance point
Base shear
Displacement
(kN)
(mm)
978.56
86.29
1091.33
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96.08
Location of hinges
BIO
A-B
IO
-LS
186
32
5
146
48
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224
International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
Medium
Soft
Yield
774.79
89.92
192
24
6
0
2
224
Ultimate
981.63
101.86
164
24
6
20
10
224
Yield
559.96
96.86
192
30
2
0
0
224
Ultimate
713.42
111.71
172
18
14
8
12
224
TABLE IV
PERFORMANCE POINT AND LOCATION OF HINGES FOR BARE FRAME BUILDING WITH USER DEFINED HINGES
Equivalent Static Method
Soil type
No of
stoteys
Performance point
Base shear
(kN)
Location of hinges
Displacement
(mm)
A-B
B-
IOLS
LSCP
CP
to E
TOT
AL
IO
Yield
901.12
92.31
180
38
6
0
0
224
Ultimate
1002.28
104.36
146
52
20
2
4
224
Yield
704.25
96.56
192
28
4
0
0
224
Ultimate
894.47
110.91
168
23
6
22
5
224
Yield
498.42
104.35
198
22
4
0
0
224
Ultimate
637.3
124.97
172
14
20
7
11
224
Hard
Medium
Soft
Response Spectrum Method
Soil type
No of
stoteys
Performance point
Base shear
(kN)
Location of hinges
Displacement
(mm)
A-B
B-
IOLS
LSCP
CP
to E
TOT
AL
IO
Yield
931.97
90.81
186
32
6
0
0
224
Ultimate
1037.39
101.36
146
52
18
2
6
224
Yield
735.1
95.06
192
24
8
0
0
224
Ultimate
929.58
107.91
164
24
6
24
6
224
Yield
529.27
102.85
192
30
2
0
0
224
Ultimate
672.41
118.97
172
18
18
6
10
224
Hard
Medium
Soft
TABLE V
PERFORMANCE POINT AND LOCATION OF HINGES FOR SOFT STOREY BUILDINGS WITH DEFAULT HINGES
Equivalent Static Method
Performance Point
Soil type
Hard
Medium
Soft
Base shear (kN)
Displacement (mm)
Yield
1299.97
32.491
Location of hinges
BIOA-B
IO
LS
279
5
0
Ultimate
1681.11
131.503
272
10
1
0
1
284
Yield
1037.08
36.434
276
8
0
0
0
284
Ultimate
1751.75
139.463
261
7
2
13
1
284
Yield
847.674
40.194
277
7
0
0
0
284
Ultimate
1522.08
324.906
260
5
4
0
15
284
No of stoteys
LSCP
0
CP to
E
0
TOTAL
284
Response Spectrum Method
Performance point
Soil type
No of stoteys
Base shear (kN)
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Displacement (mm)
Location of hinges
BIOA-B
IO
LS
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LSCP
CP to
E
TOTAL
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International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
Hard
Medium
Soft
Yield
Ultimate
Yield
Ultimate
Yield
Ultimate
1467.49
1663.89
852.37
1237.64
724.96
891.84
101.37
110.49
109.24
112.7
116.36
119.7
260
245
266
248
273
251
18
12
14
11
6
15
5
12
2
13
3
10
1
2
2
2
1
0
0
13
0
10
1
8
284
284
284
284
284
284
TABLE VI
PERFORMANCE POINT AND LOCATION OF HINGES FOR SOFT STOREY BUILDINGS WITH USER DEFINED HINGES
Equivalent Static Method
Performance point
Soil Type
Hard
Medium
Soft
Base shear (kN)
Displacement (mm)
Yield
1367.41
108.41
Location of hinges
BIOA-B
IO
LS
262
18
4
Ultimate
1544.94
120.2
242
15
14
4
9
284
Yield
776.77
117.57
268
14
2
0
0
284
Ultimate
1133.29
126.32
244
14
12
4
10
284
Yield
652.68
122.69
268
10
6
0
0
284
Ultimate
803.39
132.56
248
18
13
2
3
284
No of stoteys
LSCP
0
CP to
E
0
TOTAL
284
Response Spectrum Method
Performance point
Soil type
Hard
Medium
Soft
No of stoteys
Location of hinges
260
BIO
18
IOLS
6
LSCP
0
CP to
E
0
116.8
245
12
14
4
9
284
807.169
115.971
266
14
4
0
0
284
Ultimate
1168.69
120.023
248
14
12
4
6
284
Yield
683.282
124.19
273
8
3
0
0
284
Ultimate
838.986
127.35
251
15
12
2
4
284
Base shear (kN)
Displacement (mm)
A-B
Yield
1397.61
106.71
Ultimate
1580.14
Yield
For soft storey building models the base shear decreases by
1.104 times for building models on medium soil compared to
hard soil by ESPA, there is increase in base shear by 1.04
times for soft soil. Similarly the base shear decreases by 1.344
and 1.866 times for hard and soft soils when compared to hard
soil by RSPA.
It is seen in Tables IV and VI that there is decrease in base
force at the ultimate state for both bare and soft storey frames.
The decrease in base shear for the bare frame building models
supported on medium and soft soil with user defined hinges
are found 1.120 and 1.57 times when compared to the building
models supported on hard soil by ESPA. Similarly the base
shear decreases 1.11 and 1.54 times by RSPA. For soft storey
building models the base shear decreases by 1.36 and 1.923
times for building models on medium and soft soil compared
to hard soil by ESPA. Similarly the base shear decreases by
1.315 and 1.88 times for hard and soft soils when compared to
hard soil by RSPA.It is further observed that, for the building
models with default hinges, the hinges are formed within the
life safety range at the ultimate state are 98.66%, 97.76%, and
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TOTAL
284
95.98% for bare frame building models on hard, medium, and
soft soil respectively. Similarly 98.23%, 96.83% and 94.71%
for infill frame building models on hard, medium, and soft
soils by ESPA. Similarly 96.42%, 95.53% and 94.64%, for
bare frame and 97.18%, 96.47%, and 95.77% for infill frames
by RSPA respectively. The hinges are formed beyond the CP
range at the ultimate state is 1.33%, 2.23%, and 4.01% for
bare frame building models on hard, medium, and soft soil
respectively. Similarly 1.76%, 3.16%, and 5.28% for infill
frame building models on hard, medium and soft soils by
ESPA. Similarly 3.57% and 4.46% and 5.35% for bare frame
and 2.81%, 3.52%, and 4.22% for infill frames by RSPA
respectively.
It is further observed that, for the building models with user
defined hinges, the hinges are formed within the life safety
range at the ultimate state are 98.21%, 97.76%, and 95.98%
for bare frame building models on hard, medium, and soft soil
respectively. Similarly 96.83%, 96.47% and 98.94% for infill
frame building models on hard, medium, and soft soils by
ESPA. Similarly 97.32%, 96.42%, and 95.53% for bare frame
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International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
and 98.59%, 97.18% and 95.42% for infill frames by RSPA
respectively. The hinges are formed beyond the CP range at
the ultimate state is 1.78%, 2.23%, and 4.91% for bare frame
-building models on hard, medium, and soft soil respectively.
Similarly 3.16%, 3.52%, and 1.05% for infill frame building
models on hard, medium and soft soils by ESPA. Similarly
3.57% and 4.46% and 5.35% for bare frame and 1.40%,
2.81%, and 4.57% for infill frames by RSPA respectively.
The performances of the bare frame and soft storey building
supported on medium and soft soil are within the life safety at
the ultimate state for both equivalent and response spectrum
pushover method with default and user defined hinges. As the
collapse hinges are few, retrofitting can be completed quickly
and economically without disturbing the incumbents and
working of the buildings.
B. Ductility Ratio (DR)
The ability of the structure or its component, or the material
used to offer resistance in the inelastic domain of response is
described by the term ductility. This is important for an
earthquake resisting system because if the structure is
incapable of behaving in ductile fashion then it should be
designed for higher seismic forces. The ductility ratio (DR)
values are given in Table VII and VIII
Ductility factor  is the ratio of total imposed displacement 
at any instant to that at the onset of yields  y i.e.  = / y >1
[12].
Soft
104.35
124.97
1.20
122.69
132.56
1.08
Response Spectrum Method
Hard
90.81
101.36
1.12
106.71
116.8
1.09
Medium
95.06
107.91
1.14
115.97
120.02
1.03
Soft
102.85
118.97
1.16
124.19
127.35
1.03
For bare and soft storey building models on hard, medium,
and soft soil, there is no significant variation in the ductility
ratio is observed by ESPA and RSPA with user defined hinges.
Similar pattern can be observed for the building models
supported on hard, medium, and soft soil by RSPA. The
variation in ductility ratio is found to be very less for other
building models. It is concluded from the results that the
buildings are more ductile as evaluated by RSM compared to
ESM. DR in remaining models are nearer to target value.
These results reveal that as the soil stiffness decreases DR
nearer or slightly more than the target value.
C.
Safety ratio (SR)
The ratio of base shear force at performance point to the base
shear by equivalent static method is called safety ratio. If the
safety ratio is equal to one then the structure is safe, if it is less
than one than the structure is unsafe and if ratio is more than
one then the structure is safer [13]. The safety ratio values are
given in Table IX and X
TABLE VII
TABLE IX
DUCTILITY RATIO FOR BUILDING MODELS WITH DEFAULT
HINGES
SAFETY RATIO BY RESPONSE SPECTRUM PUSHOVER ANALYSIS
WITH DEFAULT HINGES
Equivalent Static Method
Equivalent Static Method
Bare frame
Type of
soil
Soft storey
IY
CY
DR
IY
CY
DR
Hard
150.11
317.84
2.12
32.491
131.503
4.05
Medium
115.47
257.571
2.23
36.434
139.463
3.83
Soft
88.697
350.248
3.95
40.194
324.906
8.08
SR
Hard
Bare frame
Base
Base
Shear
Force
1904.64 231.31
Medium
1360.46
314.59
Soft
732.581
314.59
Type of
soil
Response Spectrum Method
86.29
96.08
1.11
101.37
110.49
1.09
Medium
89.92
101.86
1.13
109.24
112.7
1.03
Soft
96.86
111.71
1.15
116.36
119.7
1.03
TABLE VIII
DUCTILITY RATIO FOR BUILDING MODELS WITH USER DEFINED
HINGES
Equivalent Static Method
Bare frame
IY
CY
IY
1751.75
438.36
4.00
2.33
1522.08
424.15
3.59
3.96
Soft
713.42
Hard
CY
231.31
4.72
1663.89
424.15
3.92
314.59
3.12
1237.64
438.36
2.82
314.59
2.27
891.84
424.15
2.10
TABLE X.
SAFETY RATIO BY RESPONSE SPECTRUM PUSHOVER ANALYSIS
WITH USER DEFINED HINGES
Equivalent static Method
DR
Hard
92.31
104.36
1.13
108.41
120.2
1.11
Medium
96.56
110.91
1.15
117.57
126.32
1.07
ISSN: 2231-5381
Medium
1091.3
3
981.63
Soft storey
DR
4.32
Response Spectrum Method
Hard
Type of
soil
SR
8.23
Soft storey
Base
Base
Shear
Force
1681.11 424.15
Type of
soil
Bare frame
Base
Shear
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Soft storey
Base
Force
SR
Base
Shear
Base
Force
Page 125
SR
International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
Hard
1002.28
231.31
4.33
1544.94
424.15
3.64
TABLE XI
Medium
894.47
314.59
2.84
1133.29
438.36
2.59
GLOBAL STIFFNESS BY EQUIVALENT STATIC PUSHOVER
ANALYSIS WITH DEFAULT HINGES
Soft
637.3
314.59
2.03
803.39
424.15
1.89
Equivalent Static Method
Response Spectrum Method
Bare frame
BF at
Disp.
PF
at PF
Soft storey
Disp. at
PF
Hard
1037.39
231.31
4.48
1580.14
424.15
3.73
Medium
929.58
314.59
2.95
1168.69
438.36
2.67
Type of
soil
GS
BF at
PF
1.98
Hard
1904.64
317.84
5.99
1681.11
131.503
12.78
Medium
1360.46
257.57
5.28
1751.75
139.463
12.56
Soft
732.581
350.25
2.09
1522.08
324.906
4.68
Soft
672.41
314.59
2.14
838.986
424.15
It is observed that, SR of the bare frame building models
supported on the hard, medium, and soft soil by ESPA with
default hinges are found 1.74, 1.38, and 1.026 times safer
compared to the building models evaluated by RSPA.
Similarly, soft storey buildings by ESPA are found 1.01, 1.42
and 1.79 times safer to the building models evaluated by
RSPA.
It is further observed that, SR of the bare frame building
models supported on the hard, medium, and soft soil by RSPA
with user defined hinges are found 1.034, 1.03 and 1.05 times
safer compared to the building models evaluated by ESPA.
Similarly soft storey buildings by RSPA are found 1.02, 1.03
and 1.04 times safer when compared to the ESPA models. As
the safety ratio values are greater than one, the building
models are safer.
D.
Response Spectrum Method
Hard
1091.33
96.08
11.36
1663.89
110.49
15.06
Medium
981.63
101.86
9.64
1237.64
112.7
10.98
Soft
713.42
111.71
6.39
891.84
119.7
7.45
TABLE XII
GLOBAL STIFFNESS BY EQUIVALENT STATIC PUSHOVER
ANALYSIS WITH USER DEFINED HINGES
Equivalent Static Method
Type of
soil
Global stiffness (GS)
The ratio of base shear to the displacement at performance
point is called as global stiffness [13]. In present study the
stiffness parameter is studied in order to understand the
behaviour of the building in terms of strength due to applied
earthquake load. The global stiffness values are shown in
Table XI and XII
It is observed from the Tables XI to XII that GS of the bare
frame building models supported on hard, medium, and soft
soil by RSPA with default hinges are increased by 1.89, 1.825
and 3.05 times when compared to the building models
evaluated by ESPA with default hinges. Similarly GS of soft
storey buildings by RSPA are increased by 1.18 and 1.59
times when compared to the ESPA. It is further observed that
GS of bare frame building models by RSPA are increased by
1.065, 1.06, and 1.1 times when compared to ESPA models.
Similarly the soft storey models by RSPA are increased by
1.05, 1.08 and 1.08 times when compared to ESPA models
with user defined hinges.
The global stiffness decreases with stiffness of the soil. It can
be concluded the buildings are stiffer on medium soil
compared to buildings on soft soil. Further these results reveal
that, multistoreyed RC multistoreyed buildings designed
considering earthquake load combinations prescribed in
earthquake codes are stiffer to sustain earthquakes.
CONCLUSIONS
Based on the building considered, soil parameters, procedure
followed and results obtained, the following conclusions are
drawn.
ISSN: 2231-5381
GS
Hard
Mediu
m
Soft
Hard
Mediu
m
Soft
1.
2.
3.
4.
5.
Bare frame
Displa
BF at
cemen
PF
t at
PF
1002.28 104.36
Soft storey
GS
BF at
PF
Displac
ement
at PF
GS
9.6
1544.94
120.2
12.85
894.47
110.91
8.06
1133.29
126.32
8.97
637.3
124.97
5.1
803.39
132.56
6.06
116.8
13.52
Response Spectrum Method
10.2
1037.39 101.36
1580.14
3
929.57
107.91
8.61
1168.68
120.02
9.73
672.4
118.96
5.65
838.98
127.35
6.58
Stiffness of masonry infill walls must be considered
during design of structure to capture true results to
avoid damage to earthquake shaking.
The observations clearly indicate that the user-defined
hinge model is superior than the default-hinge model
in reflecting nonlinear behaviour of the structure.
The base shear at the performance point decreases as
the soil property changes from hard to soft.
The models considered in this paper are safer, ductile,
stiffer, and more than 90% of hinges are developed
within life safety level by equivalent static pushover
analyses with default and user defined hinges.
The safety ratio is greater than one indicates that both
bare and soft storey buildings are safer.
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Page 126
International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 3 – Aug 2014
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