Effect of Soil Structure Interaction on Buildings with Mass Irregularity under Seismic Load

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 07 | July -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 876
Effect of Soil Structure Interaction on Buildings with Mass Irregularity
under Seismic Load
Mr. Kotkar R.K.1, Prof. Patankar J. P.2
1 Student, Department of Applied Mechanics, WCE, Sangli, Maharashtra, India)
2proffessor Department of Applied Mechanics, WCE, Sangli, Maharashtra, India)
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Abstract - The main objective of the study is to investigate
the significance of effect of soil structure interaction on
building with mass irregularity. In the present study the
behavior of building with mass irregularity is considered. To
address this problem, a Finite Element Method is used to
model soil structure interaction analysis of foundation and
supported framed structures by SAP 2000 V18 software. An
attempt has been made to evaluate the effect of soil structure
interaction on building with mass irregularity by considering
the systematic parameters like time period, baseshear, lateral
displacement, storey drift. Response spectrum analysis has
been carried out and the parameters like time period, base
shear, roof top displacement and storey drift of the building
frames resting over foundation and soil media has been
studied.
Key Words: soil structure interaction, vertical irregularity,
mass irregularity, response spectrum.
1. INTRODUCTION
An earthquake cause, failure of structure which starts at
points of weakness. Discontinuity in mass, stiffness and
geometry of structure cause weaknesses in structure. The
structures which having such type of discontinuity are
termed as Irregular structures. Building with vertical
irregularities are one of the major reasons of failures of
structures during earthquakes. Structures with soft storey
were the most notable structures which collapsed. Such
effect of vertical irregularities in the seismic performance of
structures becomes very important. Changesin height-wise
stiffness and mass cause the dynamic characteristics of
these buildings different from the regular‘ building. IS 1893
definition of Vertically Irregular structures: The irregularity
in the building structures may be due to irregular
distributions in their mass, strength and stiffness along the
height of building. When such buildings are constructed in
high seismic zones, the analysis and design becomes more
complicated. So the effect of soil structure interaction effect
cosideration is most important parameter.
1.1 Soil-Structure Interaction (SSI)
Soil-Structure Interaction (SSI) is phenomena in the
response of structures caused by the flexibility of the
foundation soils, as well as in the responseofsoils caused by
the presence of structures. Analytic and numerical models
for dynamic analysis typically ignore SSI effects of the
coupled in nature structure foundation-soil system. It has
been recognized that SSI effects may have a significant
impact especially in cases involving heavier structures rest
on soft soil conditions.
1.2 Mass Irregular Building
According to IS 1893-2002, mass irregularity shall
be considered to exist where the seismic weight of any
storey is more than 200 percent of that of its adjacent
storeys. The irregularity need not be considered in case of
roofs.
2. OBJECTIVE OF STUDY
Study of soil structure interaction due to seismic load
having vertical irregularity with different types of soils viz.
soft, medium and hard, using software consists of
1. Modeling and analysis of regular building and building
with mass irregularity withoutandwithconsideringsoil
structure interaction with different types of soils.
2. Comparison of above responses ofregularbuildingsand
irregular buildings on different types of soils like base
shear, time period, top storey displacement and storey
drift.
3. PROBLEM FORMULATION
For this study, an 11-storey with 5 bays frame (Each
bay span 6 m) and floor height 3.0m, regular in plan is
considered. This building is considered to be situated in
seismic zone ‘iv’ and designed in compliance to the Indian
Code of Practice for Earthquake Resistant Design of
Structures. The buildingismodeledusingsoftwareSAP2000
and analyzed by response spectrum method.. Model is
studied for comparing, base shear, time period, top storey
displacement and storey drift as follow:
following models are considered for this study.
1) Regular building and
2) Three models with mass irregularity having same total
seismic weight are considered. Heavy mass considered at
bottom, middle and top storey.

3.2 Models
Model 1 Model 2
(Regular Building) (Mass at Bottom Storey)
Model 3 storey)
Model 3 Model 4
(Mass at Middles Storey) (Mass at Top Storey)
Figure 1 regular building and mass irregular buildings
3.2 Common Data for All Models
Table 1 Building Data for Problem
Table 2 Gravity Loads Assigned to RC Building
Gravity Load Value
Slab Load (dead load) 3.75
kN/m2
Floor Finish 1 kN/m2
Roof Finish 1.0 kN/m2
Live Load 3.0 kN/m2
Roof Live 1.5 kN/m2
Wall Load 9.6 kN/m
Heavy weight for mass irregular
building
18 kN/m2
No. of stories 11
Floor to Floor Height 300 mm
Beam size 200 mm X 600 mm
Column size 700 mm X 700 mm
Thickness of slab 150 mm
Density of the concrete 25 ken/m3
Soil Type Medium
Zone factor (Z) 0.24
Importance factor (I) 1
Response reduction factor (R) 3

Table 3 Foundation Parameters
Table 4 Stiffness of Equivalent Soil Spring (KN/m)(ref.
FEMA 356)
Foundation size:-
Length of footing L=4.5 m
Width of footing B=4.5 m
Depth of footing d =0.9 m
depth of foundation from ground level D=4m
4. RESULT AND DISCUSSION
Response Spectrum Analysis is carried out for Bare frame.
The models are checked for time period, base shear, and
maximum top displacement.
Chart 1 Comparison of Time Period for Regular and Mass
Irregular Building
Chart 2 Comparison of Base Shear for Regular and Mass
Irregular Building
Chart 3 Comparison of Top Storey Displacement for
Regular and Mass Irregular Building
Soil
type
Designation Modulus of
elasticity
(KN/m2)
Poisson’s
ratio( )
Hard
soil
E-65000 65000 0.3
Medium
soil
E-35000 35000 0.4
Soft soil E-15000 15000 0.4
Soil type E-65000 E-35000 E-15000
Translation
along x-axis(Kx)
536972.88 285266.84 122257.22
Translation
along y-axis(Ky)
536972.88 285266.84 122257.22
Translation
along z-axis(Kz)
334731.70 195260.16 83682.93
Rocking about x-
axis(Kox)
626095.10 365222.14 156523.77
Rocking about y-
axis(Koy)
716522.96 417971.73 179130.74
Torsion about z-
axis(Koz)
971272 485636 208129.71

Chart 4 Comparison of Storey Drift for Regular and Mass
Irregular Building for Fixed Condition
Irregular Building for Hard Soil Condition
Irregular Building for Medium Soil Condition
Irregular Building for Medium Soil Condition
1. From chart 1, found that natural period of structure
increases when mass vary from bottom storey to top
storey. It is critical for mass is at top floor. Rate is
higher for soft soil. it is 29.62% w.r.t regular building
fixed support condition for mass at top storey.
2. From chart 2 ,it is found that increase in soil flexibility
causes decrease in base shear in both directions as
mass changes from bottom storey to top storey. For
soft soil base shear decreases with higher rate. Base
shear decreases up to 22.14% w. r. t. regular building
with fixed support condition for mass at top storey.
3. From chart 4 found that, roof displacement is also
observed to be increases when mass vary from
bottom storey to top storey. For soft soil roof
displacement is higher than fixedsupportcondition.It
increases up to 54.68% w. r. t. regular building with
fixed support condition for mass at top storey.
4. From chart 4 to 7 found that storey drift is maximum
for mass is at middle storey. It is increases from fixed
support condition to soft soil condition.
5. CONCLUSION
1. For building with mass irregularity, base shear
decreases when mass move from bottom storey to top
storey also from fixed support condition to soft soil
condition.
2. For building mass irregularity natural period,topstorey
displacement and storey drift of building increases
when mass vary from bottom storey to top storey also
from fixed support condition to soft soil condition.

REFERENCES
[1] Sekhar Chandra Dutta, Koushik Bhattacharya and Rana
Roy (2004), “Response of low-rise buildings under
seismic ground excitation incorporating soil–structure
interaction” Soil Dynamics and Earthquake Engineering
24, pp 893–914.
[2] Jinu Mary Mathew, Cinitha A, Umesha P K, NageshRIyer
and Eapen Sakaria (2014), “Seismic response of RC
building by considering soil structure interaction”
International Journal of Structural & Civil Engineering,
Res. ISSN 2319 – 6009 Vol. 3, pp 160-172
[3] S. A. Halkude, Mr. M. G. Kalyanshetti, Mr. S. H. Kalyani
(2014), “Soil Structure Interaction Effect on Seismic
Response of R.C. Frames with Isolated Footing”,
International Journal of Engineering Research and
Technology, Vol. 3 Issue 1, pp 2767-2775
[4] Shehata E. Abdel Raheem, Mohamed M. Ahmed and
Tarek M. A. Alazrak (2015), “Evaluation of soil–
foundation–structure interaction effects on seismic
response demands of multi-story MRF buildings on raft
foundations”, Advance Structural Engineering., pp 11-
30
[5] Cinitha.A, Umesha P. K and Nagesh R. Iyer (2015), “Soil
structure interaction analysis for seismic responseofan
asymmetric RC building”, International Conference on
Computer Modeling and Simulation., pp 1-6

Effect of Soil Structure Interaction on Buildings with Mass Irregularity under Seismic Load

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