Seismic Analysis of a High-rise RC Framed Structure with Irregularities

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 1338
Seismic Analysis of a High-rise RC Framed Structure with Irregularities
Kusuma B
Assistant Professor, Department of Civil Engineering, Dayananda Sagar Academy of Technology and Management,
Karnataka, India
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Abstract - The paper aims at evaluatingtheseismicactions by
considering various codal provisions, which are particularly
provided for the analysis of RC building with unsymmetrical
configuration and with different types of irregularities. The
analysis is carried out on a model of G+49 stories of RC framed
structure with unsymmetrical floor plan located in Zone IV,
soil type III, using finite element based ETABS (V 13.1)
software. The various structural response parameterssuchas,
storey displacement, storey drift, base shear and storey
stiffness are determined by considering differentirregularities
such as mass irregularity, vertical geometric irregularity, re-
entrant corner, diaphragm discontinuity and stiffness
irregularity in the model and the structuralparametersstated
above are compared for the models having different
irregularities. Seismic analysis is carried out using response
spectrum method for both symmetrical and unsymmetrical
building. The extensive literature survey is carried out by
referring to the technical journal papers, books, articles, etcto
familiarize with fundamental concept of the topic. The need
for research is identified and the procedure to carry out the
analysis is formulated. The data required for the input is
collected from IS code 1893 (Part I):2002. Then the analytical
work is carried out as per the procedure formulated and the
results are obtained and varied conclusionsare arrivedat. The
major part of the study includes the comparison of values of
set of response parameters suchas, modeperiod, storeylateral
displacement, storey drift, base shear and the storey stiffness.
Key Words: Multi-storey building, unsymmetrical
configuration, ETABS V,SeismicPerformance,structural
response parameters.
1. INTRODUCTION
The effect of dynamic actions on the buildings on account of
earthquake forces (lateral forces) are very much important
from the structural engineers view point. The unique
philosophy of structural design uses force as the basis for
design. In the earthquake design, the building is subjected to
a random ground motion or vibration at its base, which
causes inertia forces in the building that in turn induce
stresses; this is referred to as the displacement type loading
also expressed as load-deformationcurveofthebuilding ora
structure.
The four important virtues of buildings or structure that
architects and the design engineers shouldlook intoinorder
to create an earthquake - resistant building design, are
namely, structural configuration, lateral stiffness, lateral
strength and ductility. These aspects can be followed by the
building design codes. But, the seismic structural
configuration can be taken care of by adopting the following
architectural features or characteristics that result in
improved structural behavior during shocks.
2. OBJECTIVES:
The present work aims to understand the importance of
codal provisions, provided for irregular RC structures.
1. Analysis of 50 storied RC framed structure with different
irregularities under seismic conditions. Irregularities
considered are Re-entrant corner, mass irregularity,vertical
geometric irregularity, diaphragm irregularity and stiffness
irregularity.
2. Study the effect of seismic responses such as the storey
lateral displacement, storey drift, storey shear, storey
stiffness and mode period in zone IV.
4) To propose the best suitable building plan configuration
in the existing condition.
3. LITERATURE REVIEW :
Sanjay Kumar Sadhu and Dr. Umesh Pendharkar studiedthe
effect of Aspect Ratio and plan configurations on seismic
performance of multi-storeyedregularR.C.C.buildings.They
found that Seismic parameters increase with number of
bays and number of storeys. Also Square configuration
(horizontal aspect ratio=1) gives better performance and
Vertical aspect ratio should be kept less than 4.
M Anvesh, Shaikh and Pavan Kumar studied the Effect of
mass irregularity on RCC framed structure (G+10). They
observed that size of structural members increase in mass
irregular structure thus consuming more steel.
Ankesh Sharma and Biswobhanu Bhadra carried out
Seismic analysis of vertically irregular RCC frames (G+10)
They observed an increase in Base shear for mass irregular
structure, large inter-storey drift in stiffness irregular
structure
And also large displacementingeometricirregularstructure.
Dileshwar Rana,Prof.Juned Raheem studiedseismicanalysis
of regular & vertical geometric irregular RCC framed
building. They concluded that 4 bay frames is appropriate
for lower building height and for higherstories,8bayframes

is suitable.Seismic performance improves with number of
bays.
Shaikh Abdul Aijaj, Abdul Rahman and Girish Deshmukh
performed a study on seismicresponseofverticallyirregular
RC frame with stiffness irregularity at fourth floor: they
found large displacements.
4. METHODOLOGY
To study the effect of earthquake on a high-rise RC framed
structure by considering different irregularities in
earthquake seismic zone IV as per IS code 1893 (Part
I):2002.
Following steps of methods of analysis are adopted in this
study:
Step-1: Selection of the structures with different
irregularities.
Step-2: Selection of seismic zone (IV).
Step-3: Formation of load combinations.
Step-4: Modelling of building frames using ETABS-V
software.
Step-5: Equivalent static Analysis of all the models.
Step-6: Comparative studyof results(seismic parameters)in
terms of Storey lateral displacement and storey drift, Base
shear, Storey stiffness, Mode Period.
5. STRUCTURAL MODELING:
In this study, 4 types of building configurations have been
considered:Massirregularity,Re-entrantcornerirregularity,
Vertical geometric irregularity, Stiffness irregularity.
Table 1: Details of Base Model
No. of stories 50
Height of the building (m) 150
Storey Height (m) 3
Plan Dimension (m) 50 * 50
Vertical aspect ratio 3
Horizontal aspect ratio 1
Bay width (m) 6
Beam dimension (mm) 300 * 450
Column dimension (mm) 800 * 800
Earthquake zone IV
Type of Analysis Equivalent static lateral
force
Soil type III (IS:1893-2002)
Zone factor 0.24 (Clause6.4.2ofIS:1893-
2002)
Importance factor 1 (Table 6, Clause 6.4.2 of IS:
1893-2002)
Response reduction factor 5 (SMRF) (Table 7 of
IS:1893-2002)
Table 2: Section and Loading Properties of model
Section Properties
Column size 800 * 800 mm
Beam size 300 * 450 mm
Slab thickness 150 mm
Wall thickness 200 mm
Loading Properties
Live load 2 kN/m2
SDL 2 kN/m2
Specific weight of RCC 25 N/m2
6. RESULTS AND DISCUSSIONS:
6.1. Comparison of irregular structures with respect to
regular structure:
1. The mode period is found very high for stiffness irregular
and is less for diaphragm discontinuity compared to that of
the regular structure. This is because of the reduction in
stiffness (k) of the irregular structure.
T = 2π √m/k
2. The lateral displacement is found very high for re-entrant
corner structure compared to regular structure. This is due
to change in geometry of the structure and also due to
decrease in stiffness of the structure.
3. Storey drift is very high for irregular structurescompared
to regular structure.
4. Base shear (VB) is found high formassirregularstructure,
but is found less for vertical geometric irregular, diaphragm
discontinuity structure. This is due to increase in seismic
mass (3.23%) of mass irregular structure (VB = A * W)
5. Storey stiffness is found high for regular structure
compared to irregular structures which is due to reduction
in stiffness of irregular structures.

6.2 Comparison of irregular structures:
1. The mode period is found more for stiffness irregular
structure, compared to other irregular structures (mass
irregular, re-entrant corner, vertical geometric irregular,

diaphragm discontinuity) because of reduced stiffness of
stiffness irregular structure, as the height of storey is
increased and also due to increase in mode period.
2. The storey lateral displacement is found very high for re-
entrant corner structure compared to other irregular
structures (mass irregular, re-entrant corner, vertical
geometric irregular structure). This is due to change in
geometry of the structure and the inertial forces are more
and hence displacement is more.
3. The storey drift is very high for re-entrant corner
structure compared to other irregular structures (mass
irregular, re-entrant corner, vertical geometric irregular
structure). This is due to change in geometry of the
structure, leading to reduction in stiffness and the inertial
forces are more due to increased mode period.
4. The base shear is found very high for mass irregular
structure compared to other irregular structures (mass
irregular, re-entrant corner, vertical geometric irregular
structure). This increase in base shear is due to increase in
seismic mass of the structure and also increase in mode
period and inertial forces of the structure.
5. The storey stiffness is found very low for re-entrant
corner structure compared to other irregular structures
(mass irregular, re-entrant corner, vertical geometric
irregular structure). This decrease in stiffness is due to
change in geometry (L-shape) of the structure, increased
mode period and inertial forces of the structure.
7. CONCLUSIONS:
From the above conclusions it is clear that the regular
structure with RC momentresistingframeandwithmasonry
walls, perform better under the action of seismic load,
compared to irregular structure. The irregular structures,
especially the re-entrant corner structure shows the worst
performance when subjectedtoseismicexcitationcompared
to other type of irregular structures compared to other
irregular structures (mass irregular, mass irregular,vertical
geometric irregular structures).
The lateral displacement is increased in case of vertical
irregular structure, re-entrant corner structureandstiffness
irregular structure, from the storey where the irregularity is
introduced.

The stiffness of the structure is reduced in vertical irregular,
re-entrant corner and stiffness irregular structure.
8. REFERENCES:
1. M Anvesh, Shaikh and Pavan Kumar [1], “Effect of Mass
Irregularity on Reinforced Concrete Structure Using Etabs,”
International Journal of Innovative Research in Science,
Engineering and Technology, Vol. 4, Issue 10, October 2015.
2. Ankesh Sharma and Biswobhanu Bhadra [2], “Seismic
analysis and design of vertically irregular RC building
frames”, National Institute of Technology Rourkela.
3. Sanjay Kumar Sadhu and Dr. Umesh Pendharkar [3],
“Effect of Aspect Ratio & Plan Configurations on Seismic
Performance of Multi-storeyed Regular R.C.C. Buildings”: An
Evaluation by Static Analysis. International Journal of
Emerging Technology and Advanced Engineering Website:
www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified
Journal, Volume 6, Issue 1, January 2016).
4. Dileshwar Rana, Prof. Juned Raheem[4],“Seismic Analysis
of Regular & Vertical Geometric Irregular RCC Framed
Building” . International ResearchJournal ofEngineering and
Technology (IRJET) e-ISSN: 2395-0056Volume:02Issue:04
| July-2015
5. Shaikh Abdul Aijaj, Abdul Rahman and Girish Deshmukh
[5], “Seismic Response of Vertically Irregular RC Framewith
Stiffness Irregularity at Fourth Floor”. International Journal
of Emerging Technology and Advanced Engineering (ISSN
2250-2459,ISO 9001:2008 CertifiedJournal,Volume3,Issue
8, August 2013)
6 Mohammed Yousuf, P.M. Shimpale [6], “Dynamic Analysis
of Reinforced Concrete Building with Plan Irregularities”.
International Journal of Emerging TechnologyandAdvanced
Engineering Website: www.ijetae.com(ISSN 2250-2459,ISO
9001:2008 Certified Journal, Volume 3, Issue 9, September
2013) .
7. Prof. Milind and V. Mohod [7], “Analysis of Structures
with Plan Irregularity.” IOSR Journal of Mechanical and Civil
Engineering (IOSR-JMCE) e-ISSN: 2278-1684,p-ISSN: 2320-
334X, Volume 12, Issue 4 Ver. VII (Jul. - Aug. 2015)
8. IS1893: (Part I)-2002 “Criteria for Earthquake resistant
design of structures” Bureau of Indian Standards
AUTHOR’S PROFILE
Prof. Kusuma B. Sheiscurrentlythe
Assistant Professor, Civil
Engineering Department at
Dayananda Sagar Academy of
Technology and Management,
Bangalore, Karnataka. She has done
her under graduation andMastersat
Dayananda Sagar College of
Engineering, Bangalore, Karnataka.

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