IRJET- Study of Literature on Seismic Response of RC Irregular Structure

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 04 | Apr 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 3721
STUDY OF LITERATURE ON SEISMIC RESPONSE OF RC IRREGULAR
STRUCTURE
Ashwin R. Dhabre1 & Dr. N.R. Dhamge2
1M.Tech student, Civil Engineering Department, KDK College of Engineering, Nagpur
2Professor, Civil Engineering Department, KDK College of Engineering, Nagpur
----------------------------------------------------------------------***-----------------------------------------------------------------------
Abstract - In multi-storeyed framed building damage
occurring from earthquake ground motion generally
initiates at locations of structural weaknesses present in the
lateral load resisting frames. In some cases these weaknesses
may be created by discontinuities in stiffness, mass between
adjacent storeys. Such discontinuities between storeys are
often associated with sudden variations in the vertical
geometric irregularity. Vertical irregularity are structures
with soft stories which can further be broken down into the
different types of irregularities as well as their severity for a
more refined assessment tool pushover analysis which is one
of the method available for evaluating building against
earthquake loads. A structure is induced incrementally with
a lateral loading pattern until the structure lateral loading
pattern until the structure reaches a limit state. The model is
then modified to account for the reduced stiffness of the
building and is once again applied with a lateral load unit
additional member’s yield. A base shear vs. displacement
capacity curve and a plastic hinging model is produced as
the end product of analysis which gives a general idea of the
behavior of the building. In the building frame is designed as
per Indian standard i.e. IS-456: 2000, IS-1893: 2002 and IS-
1893: 2016. The main objective of this study the
irregularities which we need to consider while analyzing it
for the seismic loading given in IS- 1893: 2002 (Part-I) and
to compare seismic behavior of RC structure by using IS code
1893: 2016 (Part-I). The structural guideline on things such
as the computation of the target displacement and the
things to consider for a proper analysis such as the
modelling rules. The ATC-40 document is followed in this
study. Using structural analysis design SAP2000 software.
The present study is to evaluate the behavior of two typical
new R.C.C building were taken for analysis G+6 and G+11
floor reinforced concrete frame structure subject to
earthquake force in zone V. The paper gives the study of
different literature investigation taken on pushover analysis.
1. INTRODUCTION
Earthquakes pose multiple hazards to a community, failure
of structure starts at points of weakness. This weakness
increases due to discontinuity in mass, stiffness and
geometry of structure. The structures having this
discontinuity are called as Irregular structures. Vertical
irregularities are one of the main reasons of failures of
structures during earthquakes. Vertical irregularity are
buildings with soft stories. This can be further broken
down into the different type of irregularities as well as
their severity for a more refined assessment tool.
Pushover analysis is one of the methods available for
evaluating building against earthquake loads. A structure
is induced incrementally with a lateral loading pattern
until the structure reaches a limit state. The structure is
subjected to the load until some structure members yield.
The model is then modified to account for the reduced
stiffness of the building and is once again applied with a
lateral load until additional members yield. A base shear
vs. displacement capacity curve are produced the plastic
hinging model after complete the analysis which gives a
general idea of the behavior of the building.
In the building frame is designed as per Indian standard
i.e. IS-456: 2000, IS-1893: 2002 and IS-1893: 2016. The
main objective of this study the irregularities which we
need to consider while analyzing it for the seismic loading
given in IS- 1893: 2002 (Part-I) and to compare seismic
behavior of RC structure by using IS code 1893: 2016
(Part-I).
Figure 1. Manhattan city showing different irregular
buildings

2. REVIEW OF PREVIOUS STUDIES ON VERTICAL
IRREGULARITY
1. Lee and Ko (2007) Investigated the seismic response
characteristic of three 1:12 scale 17-story RC wall building
models was studied different types of irregularity at the
bottom two stories were subjected to the same series of
imitation of a situation earthquake excitations. The study
evaluated the first model has a symmetrical moment-
resisting frame (Model 1), the second has an infilled shear
wall in the central frame (Model 2), and the third has an
infilled shear wall in only one of the exterior frames
(Model 3) at the bottom two stories. Based on the test
results, which are analyzed and compared. They estimated
fundamental periods for other structures than moment
frames and bearing wall structures in UBC 97 and AIK
2000 appear to be reasonable. The large amounts of
energy absorption by damage are similar regardless of the
existence and location of the infilled shear wall. The largest
energy absorption is due to overturning, followed by that
due to shear deformation. It was also observed that rigid
upper system renders rocking behavior in the lower frame,
and its self-weight contributes up to about 23% of the
resistance against the total overturning moment.
2. Athanassiadou (2008) illustrated the influence of
irregular in elevation on the response of multistorey
reinforced concrete (R/C) frame buildings under the
seismic loading by considering Two ten-storey two-
dimensional plane frames with two and four large setbacks
in the upper floors respectively, as well as a third one
regular in elevation, have been designed to the provisions
of the 2004 Eurocode 8 (EC8) for the high (DCH) and
medium (DCM) ductility classes, and the same peak
ground acceleration (PGA) and material characteristics. All
frames have been subjected to both inelastic static
pushover analysis and inelastic dynamic time-history
analysis for selected input motions. They found that the
assessment of the seismic performance is based on both
global and local criteria. The report concluded that the
effect of the ductility class on the cost of buildings is
negligible, while the seismic performance of all irregular
frames appears to be equally satisfactory, not inferior to
that of the regular ones, even for motions twice as strong
as the design earthquake. They describe the DCM frames
are found to be stronger and less ductile than the
corresponding DCH ones. The over strength of the
irregular frames is found to be similar to that of the
regular ones, while DCH frames are found to dispose
higher over strength than DCM ones. They stated that the
pushover analysis seems to underestimate the response
quantities in the upper floors of the irregular frames.
3. Wibowoa et al (2010) studied the effects of field test
insight into the push-over load deflection and collapse
behaviour of a soft storey building. They analyze the five
storey building as being particularly vulnerable to
earthquake excitation due to the particularly weak
connections at each end of the ground floor precast
columns that constituted the soft storey. Evaluated four
field tests were undertaken to investigate the actual lateral
force deflection behaviour of the soft storey columns. They
analyzed model advanced to predict the overall force
displacement relationship that was influenced by the three
component mechanisms of (a) connection strength at
column ends, (b) gravity rocking strength and (c) ground
slab interaction, was establish to be in excellent agreement
with the experimental test results. The study reported that
the precast soft storey system was establish to been
sufficient displacement capacity for lower seismic regions,
but the performance was considered marginal for higher
seismic regions.
4. Sarkar et al. (2010) suggested a new method of
quantifying irregularity in vertically irregular building
frames, accounting for dynamic characteristics (mass and
stiffness). The salient conclusions were as follows:
(1)A part of vertical irregularity, suitable for stepped
buildings, called regularity index‘, is proposed, accounting
for the changes in mass and stiffness along the height of
the building.
(2) An empirical formula is proposed to calculate the
fundamental time period of stepped building, as a function
of regularity index.
5. Hejazi1 et al (2011) Studied the effect of serious
structural damage suffered by several modern buildings
during recent earthquakes emphasize the importance of
avoiding immediate changes in lateral stiffness and
strength. Although damage and collapse due to soft story
are most often observed in buildings, they can also be
refined in other types of structures. The lower level
accommodate the concrete columns act as a soft story in
that the columns were inadequate to provide adequate
shear resistance during the earthquake. They can be
provided most economical way of retrofitting such as a
building is by adding proper bracing to soft stories. They
has been approved to investigate on adding of bracing in
various arrangements to structure in order to decreased
soft story effect on seismic response of building. It is
advantage to assess the vulnerability level of existing
multi-storied buildings so that they can be retrofitted to
possess the minimum requirements. This will help in
minimizing the impending damages and catastrophes.

6. Kirac et al (2011) discussed the importance of base
floors of the existing buildings are generally arranged as
garages or offices. No walls are built in at these floors due
to its recommended management and comfort problems.
But upper floors do have walls divide rooms from each
other for the residential usage. In these preparation, the
upper floors of most buildings are stiffer than their base
floors. This phenomenon is called as the weak-storey
irregularity. They described the weak stories are subjected
to larger lateral loads during earthquakes and under
lateral loads their lateral deformations are greater than
those of other floors so the design of structural members
of weak stories is demanding and it should be particular
from the upper floors. The study analyzed the building
models which are consisting of various stories, storey
heights and spans. They compared the result with the
current earthquake code. The ratio of buildings which
acquire weak-storey irregularity is resolved for both
Ankara and Eskisehir regions. It is observed that negative
effects of this irregularity can be decreased by some
precautions during the construction stage. They stated that
some recommendations are presented for the existing
buildings with weak-storey irregularity.
7. Misir (2015) investigated the effects of a new type of
infill called locked brick infill adopting horizontal sliding
Joints in reducing the soft-story formation in reinforced
concrete (RC) frames with code-conforming seismic
detailing. He performed nonlinear static time-history
analyses on multistory planar frames with only the upper
stories infilled in order to force the soft-story irregularity.
The parameters of frame and infill elements that was used
in numerical simulations was obtained from half-scale RC
infilled frame tests that had been performed by the author
covering single storey single bay frames infilled with
standard and locked bricks. He stated that the numerical
reproduction showed that the use of locked bricks to form
infill walls has the potential to decrease the soft-
story/weak-story formation in comparison to standard
bricks due to its shear drift mechanism and decreased
upper-story/first-story stiffness, even in buildings that
have noninfilled first stories.
8. Arlekar et al. analyzed the seismic response of four
storey RC frame building with open ground storeys using
equivalent static analysis and response spectrum analysis
to find the resultant forces and displacements. They
argued for immediate measures to prevent the haphazard
use of soft first storeys in buildings, which are designed
without regard to the increased displacement, ductility
and force demands in the first storey columns. Some
alternate measures involving stiffness balance of the open
first storey and the stiffness above, were proposed to
reduce the irregularity introduced by the open first storey.
9. Negro and Verzeletti studied the effects of the infills on
the global behavior of the structure by performing series
of pseudo-dynamic tests on the full-scaled four-storey
reinforced concrete frame. The response of structure in
three configuration i.e. bare frame, uniform infilled frame
and partial infilled frames has been compared. They
plotted time history curve and base shear for all three
structures and concluded that the presence non-structural
masonry infills can change the response of structure to a
large extent. Irregularities in the panels were found to
result in unacceptably larger damage to the frame as a
result of high ductility demands. They also found that
masonry infill increases stiffness, strength and energy
dissipation capacity.
10. Sahoo & Rai (2013) analyzed the evaluation of two
strengthening techniques to improve the seismic
performance of the existing non-ductile RC frames with
soft-story at the ground story level. The first technique,
termed as column retrofit, uses only partial steel jacketing
to build up the lateral strength and plastic rotational
capacities of the defective columns at the ground story
level. The next technique, termed as full retrofit,
acknowledge the aluminum shear links as enhanced
energy dissipation devices in extension to the
strengthened ground story columns. Steel collector beams
and chevron braces are used to relocation the lateral load
from the RC frame to these dissipating devices. They
analyzed the Non-linear static and dynamic analyses to
evaluate the performance of the existing and the
strengthened frames. The essential parameters
investigated are (a) interstory drift, (b) residual drift, (c)
yield mechanism, (d) energy dissipation, and (e) lateral
strength. They used the full retrofit frame effectively
controlled the drift response by avoiding the soft-story
collapse because of the significant energy dissipation in
the shear links. Furthermore, the FR frame achieved the
desired yield mechanism without exceeding the design
target drift level.
3. CONCLUSION
Structure which is designed for seismic forces gives more
ductility as compare to gravity designed structure. Some
behavior is observed in both case regular and irregular
structure. Due to different behavior of structure the
nonlinear performance of structure will be affects.
Irregular structure cannot sustain more force as compared
to regular structure hence structure becomes damage.
Irregularities are harmful for the structures so it is
important to have simpler and regular shapes of frames as
well as uniform load distribution around the building. As
far as possible irregularities in a building must be avoided.

But, if Irregularities have to be introducing for any reason,
they must be designed properly.
REFERENCES
1. Han Seon Lee, Dong Woo Ko, 2007, Seismic response
characteristics of high-rise RC wall buildings having
different irregularities in lower stories, Engineering
Structures 29 (2007):3149–3167.
2. C.J Athanassiadou, 2008, Seismic performance of R/C
plane frames irregular in elevation, Engineering Structures
30 (2008):1250–1261.
3. Ari Wibowo, John L. Wilson, Nelson T. K. Lam, Emad F.
Gad, 2010, Collapse modelling analysis of a precast soft
storey building in Australia, Engineering structure 32
(2010) 1925-1936.
4. Sarkar P, Prasad A Meher, Menon Devdas, 2010,
“Vertical geometric irregularity in stepped building
frames”, Engineering Structures 32 (2010) 2175–2182.
5. F. Hejazil S. Jilani, J. Noorzaei, C.Y Chiengi, M.S. Jaafar, A.
A. Abang Ali 2011, “Effect of soft story on structure
response of high rise buildings”, Materials Science and
Engineering 17 (2011) 12043.
6. Nevzat Kirac, Mizam Dogan, Hakan Ozbasaran, “Failure
of weak-storey during earthquakes”, Engineering Failure
Analysis 18 (2011) 572- 581.
7. Ibrahim Serkan Misir, “Potential use of locked brick infill
walls to decrease soft-story formation in frame buildings”,
journal of performance of constructed facilities, 2015,
29(5).
8. Arlekar, J.N., Jain, S.K., and Murty C.V.R., “Seismic
response of RC frame buildings with soft first storey,” In
Proceedings of CBRI Golden Jubilee Conference on Natural
Hazards in Urban Habitat, New Delhi, 1997.
9. Negro, P., and Verzeletti, G., “Effect of infill on the Global
Behavior of RC Frame: Energy Considerations from
Pseudodynamic Tests,” Earthquake engineering &
structural dynamics 25 (8), 753-773, 1996.
10. Dipti Ranjan Sahoo, Durgesh C. Rai, “Design and
evaluation of seismic strengthening techniques for
reinforced concrete frames with soft ground story”,
Engineering structures 56 (2013) 1933-1944.

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