This document discusses seismic analysis of regular and irregular reinforced concrete framed buildings. It analyzes 4 building models - a regular 4-story building, a stiffness irregular building with a soft ground story, and two vertically irregular buildings with setbacks on the 3rd floor and 2nd/3rd floors. Static analysis was performed to compare bending moments, shear forces, story drifts, and joint displacements. Results showed irregular buildings experienced higher seismic demands. The regular building performed best, with the single setback building also performing well. Irregular configurations increase seismic effects and should be minimized in design.

1. 1
A Seminar on
Seismic Analysis of Regular &
Irregular RCC Framed Building
Submitted By :-
Daanish Zama
Submitted To :-
M/s Padmabati Sahoo
Asst.Professor
Civil Engineering Dept.
S I L I C O N I N S T I T U T E O F T E C H N O L O G Y
Sambalpur, Odisha

2. CONTENTS
 Introduction
 Types of Irregularities
 Objectives
 Methodology
 Problem Statement
 Structure Modelling
 Analysis of building and their Results
 Conclusion
 Reference

3. INTRODUCTIO
N
The word earthquake is used to express any seismic occurrence whether natural or caused by humans that can
produce seismic influence around any particular area. Earthquakes are caused generally by rupture of
geological faults inside the earth, but also by other events such as volcanic movement, landslides, mine
blasts, and atomic tests. Vertical irregularities are characterized by vertical discontinuities in the geometry,
distribution of mass, rigidity and strength. Setback buildings are a subset of vertically irregular buildings
where there are discontinuities with respect to geometry. However, geometric irregularity also introduces
discontinuity in the distribution of mass, stiffness and strength along the vertical direction. Majority of the
studies on setback buildings have focused on the elastic response. The behavior of these types of building is
something different. There is a need of more work to be done in this regard. So this research work is an attempt
to reach on more accurate conclusion to reduce their effect on the structure.
We observe that real structures are frequently irregular as perfect regularity is an idealization that
rarely occurs in the practice. Regarding buildings, for practical purposes, major seismic codes across the
globe differentiate between irregularity in plan and in elevation, but it must be realized that irregularity in the
structure is the consequence of a combination of both types. It is seen that irregular structural configurations
either in plan or in elevation were often recognized as one of the major causes of collapse during precedent
earthquakes.

4. TYPES OF
IRREGULARITIESThe 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. There are two types of Irregularities :-
1. Plan irregularities
2. Vertical irregularities.
Vertical irregularities are one of the major reasons of failures of structures during
earthquakes. Vertical Irregularities are mainly of five types :-
i) Stiffness Irregularity :- Under stiffness irregularity the stiffness of the members in a frame are not equal
and they vary according to the floor height, modulus of elasticity of concrete and moment of inertia
of that member.

5. Types of irregularities Cont…
ii) Mass Irregularity :- 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. In case of roof
irregularity need not be considered.
iii) Vertical Geometric Irregular :- A structure is considered to be
vertical geometric irregular when the horizontal dimension of the
lateral force resisting system in any storey is more than 200 percent
of that in its adjacent storey. In case of roofs irregularity need not be
considered.

6. OBJECTIVES
The goal of this research is to investigate various seismic responses of RC framed regular and vertical
geometric irregular structure. The comparison between various seismic parameters would allow us to
propose the best suitable building configuration on the existing condition. More specifically, the
salient objectives of this research are:
1) To perform a comparative study of the various seismic parameters of different types of reinforced
concrete moment resisting frames (MRF), configuration, and types of irregularity.
2) Comparison between regular and vertical irregular frame on the basis of shear force, bending
moment, storey drift & node displacement etc.
3) To study the change in different seismic response parameters along the increasing height and
increasing bays.
4) To propose the best suitable building configuration on the existing condition.

7. METHODOLOGY
The steps undertaken in the present study to accomplish the above-mentioned objectives are
as follows:
a) Selected an exhaustive set of regular, stiffness irregular and setback building frame models
with same heights of 4 story, assuming equal bay width of 5 m in both horizontal direction and
different irregularities.
b) Perform static analysis for each of the 4 building models taken in this study.
c) Analysing and comparison of the result of seismic analysis.
d) Presentation of results in the form of graphs and tables.
e) Detailed discussion on the results with the help of graphs and tables considering all the included
parameters.

8. PROBLEM STATEMENT

9. STRUCTURAL
MODELLING
Equivalent static analysis was performed on regular and various irregular buildings using STAAD.pro.
The storey shear forces were calculated for each floor and graph was plotted for each structure.
Three types of irregular buildings were considered, regular structure, stiffness irregular
structure (structure with ground storey as the soft storey) and two vertically geometric irregular building
with different setbacks. All the structures are of 4-storeys.
1. Regular Structure (4 storey)
2. Stiffness Irregular Structure (Soft Storey)
3. Vertical Geometric Irregular structure (setback at 3rd floor)
4. Vertical Geometric Irregular structure (setback at 2nd and 3rd floor)

10. Structural modelling
Cont…
1. Regular structure (4 storey):
Plan of regular structure 3D view of regular structure

11. Structural modelling
Cont…
2. Stiffness Irregular structure (soft
storey):
The structure is same as that of regular
structure but the ground storey has a height of
4.5m and doesn’t have brick infill.
Stiffness of each column = 12EI/l3
Therefore, Stiffness of ground floor/stiffness
of other floors = (3.5/4.5)3 = 0.47
Stiffness Irregular Structure

12. Structural modelling
Cont…
3. Vertical Geometric Irregular structure (setback at 3rd floor):The structure is 4 storeyed with setbacks
in 3rd floor. The setback is along X direction.
Width of top storey = 10 m
Width of ground storey = 15m
Vertical Geometric Irregular Structure 1. 3D view of Vertical Geometric Irregular Structure 1

13. Structural modelling
Cont…
4. Vertical Geometric Irregular structure (setback at 2nd and 3rd floor): The structure is also 4 storeyed
with setbacks in 2nd and 3rd floor. The setback is along X direction.
Width of top storey = 10 m
Width of ground storey = 15m
3D view of Vertical Geometric Irregular Structure 2Vertical Geometric Irregular Structure 2.

14. ANALYSIS OF BUILDING AND
THEIR RESULTS

15. BENDING MOMENT
for beam no.45 (vertical beam in the frame)
19
20
21
22
23
24
25
26
Regular Structure Stiffness Irregular Geometric Irregular 1 Geometric Irregular 2
Max +ve BM in Z-direction(KN-m)
Max +ve BM in Z-direction(KN-…
21.4
21.6
21.8
22
22.2
22.4
22.6
22.8
23
23.2
Regular Structure Stiffness Irregular Geometric Irregular 1 Geometric Irregular 2
Max +ve BM in Y-Direction (KN-m)
Max +ve BM in Y-Direction (KN-m)
Geometric Irregular structure frames have less critical bending
moment than Regular frames. There is not much change for the
bending moment of regular frames and stiffness irregular frames.
For geometric irregular frame with setback at 2nd & 3rd floor is
having maximum BM in Z-direction.
Same goes with the maximum bending moment in Y direction
also. Geometric Irregular structure has the less maximum as
compared to all the different structures along Y direction.

16. BENDING MOMENT
for beam no.135 (horizontal beam in the frame)
155.5
156
156.5
157
157.5
158
158.5
159
159.5
160
Regular Structure Stiffness Irregular Geometric Irregular 1 Geometric Irregular 2
Max +ve BM in Z-direction (KN-m)
Max +ve BM in Z-direction (KN-m)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Regular Structure Stiffness Irregular Geometric Irregular 1 Geometric Irregular 2
Max BM +ve in Y-direction(KN-m)
BM +ve in Y-direction(KN-m)
For beam no.135, the nature of bending moment along Z-direction is
very same as it was for the previous case. Geometric Irregular
Structure Frame has the least bending moment in comparison with all
the other three structures.
In this case, bending moment in Y-direction is totally different. It is
observed as Geometric Irregular has maximum bending moment
compared to all the structures. While in the previous cases for BM,
the geometric irregular frame 2 poses the least BM.

17. SHEAR FORCE
for beam no.45 (vertical beam in the frame)
0
2
4
6
8
10
12
14
16
18
Regular structure Stiffness Irregular Geometric Irregular 1 Geometric Irregular 2
Max +ve SF in Y-direction (KN)
Max +ve SF in Y-direction (KN)
 For shear force in Z-direction, there is no any
magnitude of maximum positive shear force
acting in z-direction.
 Geometric Irregular structure frames have
less shear force than Regular frames. There
is not much change for the bending
moment of regular frames and stiffness
irregular frames. As this conclusion is similar
with the critical seismic parameters like
bending moment.

18. SHEAR FORCE
for beam no.135 (horizontal beam in the frame)
119.8
120
120.2
120.4
120.6
120.8
121
121.2
121.4
121.6
121.8
Regular
Structure
Stiffness
Irregular
Geometric
Irregular 1
Geometric
Irregular 2
Max +ve SF in Y-direction (KN)
Max +ve SF in Y-direction (KN)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Regular Structure Stiffness Irregular Geometric Irregular 1 Geometric Irregular 2
Max +ve SF in Z-direction (KN)
Max +ve SF in Z-Direction (KN)
Same goes for the horizontal beam (beam no.135) also the shear force goes on decreasing to the geometric irregular
structure. While there is not much difference in the value of maximum shear force in both X and Z-direction.

19. STOREY DRIFT
-0.01
0
0.01
0.02
0.03
0.04
0.05
Regular Stiffness Irregular Geo.Irregular 1 Geo.Irregular 2
Storey Drift X(cm) direction
storey 1 storey 2 storey 3 storey 4
-30
-25
-20
-15
-10
-5
0
Regular Stiffness Irregular Geo.Irregular 1 Geo.Irregular 2
Storey Drift Z(cm) direction
Storey 1 Storey 2 Storey 3 Storey 4
The inter storey drift are taken in both X and Z directions.
From graph we see that the drift lines of all the 4 storeys along X
direction is almost coinciding for regular and Stiffness Irregular
frames. Regular Building configurations have exactly same value
of drift. The irregular frames Stiffness, Vertical Geometric 1,
Vertical Geometric 2 have slightly more drift in X direction
Here it is observed that the regular structure too has different storey
drift in Z-direction which was earlier same. It is observed that the
stiffness irregular frame possess higher values of drift than there
corresponding irregular frames for all the four storey height.
Also for storey 1, drift along Z-direction is almost same for all the
varieties of structure.

20. JOINT DISPLACEMENT
-0.2
0
0.2
0.4
0.6
0.8
1
Regular Stiffness
Irregular
Geo. Vertical 1 Geo. Vertical 2
Joint Displacement X(cm) direction
Storey 1 Storey 2 Storey 3 Storey 4
-30
-25
-20
-15
-10
-5
0
Regular stiffness Irregular Geo.Vertical 1 Geo. Vertical 2
Joint Displacement Z(cm) direction
Storey 1 Storey 2 Storey 3 Storey 4
It is seen that the storey displacement of 4th storey is maximum among
all the frames. However, for regular and stiffness irregular frames, the
joint displacement of all storeys are same along x-direction. And the
vertical geometric frame 2 with setbacks have maximum joint
displacement in every storey.
In this storey- 4 has maximum displacement among all the varieties
of frames. The stiffness irregular structure frame has maximum joint
displacements for all the floor levels. However, Regular and both
the vertical geometric frames have almost same joint displacement
contributing a common nature of displacement under the effects of
seismic forces.

21. CONCLUSION
Based on the work presented following conclusions can be drawn :-
1) Amount of setback increases, the shear force also increases. The regular building frames possess very low
shear force compared to setback irregular frames.
2) The critical bending moment of irregular frames is more than the regular frame for all the storey heights. This is
due to decrease in stiffness of building frames due to setbacks.
3) According to results of equivalent static method, the stiffness irregular building experienced larger inter storey
drifts as compared to regular frame and geometric irregular frames.
4) It is seen that the storey displacement of 4th storey is maximum among all the frames and the stiffness irregular
structure frame has maximum joint displacements for all the floor levels. However, regular and both the vertical
geometric frames have almost same joint displacement.
5) The seismic performance of regular frame is found to be better than corresponding irregular frames in nearly all
the cases. Therefore it should be constructed to minimize the seismic effects. Among setback frames, the geometric
irregular frame 1 building having setback at 3rd floor configuration is found superior than others.

22. REFERENCES
• Aainawala M. S., Pajgade P. S. .“Design of Multistoried R.C.C. Buildings with and without shear walls”, international
journal of engineering sciences & research technology. ISSN: 2277-9655, vol.7, no. 3, pp. [498-510].2014
• Al-Ali, A.A.K. And Krawinkler, “effects of vertical irregularities on seismic behavior of building structures”, report
no. 130, the john A. Blume earthquake engineering centre, department of civil and environmental engineering, Stanford
university, Stanford, U.S.A 1998.
• Anwaruddin m., Saleemuddin M.. “Pushover analysis of medium rise multi-story RCC frame with and without vertical
irregularity”, int. Journal of engineering research and applications, www.Ijera.Com, vol. 3, issue 5, pp.540-546.2013
• BIS (2002). “IS 1893 (part 1)-2002: Indian standard criteria for earthquake resistant design of structures”, part 1 – general
provisions and buildings (fifth revision), bureau of Indian standards, New Delhi.
• Kumar Sujit, Garg v. & Sharma a. “Effect of sloping ground on structural performance of RCC building under seismic
load”. International journal of science, engineering and technology, ISSN: 2348-4098 volume 2, issue 6. (2014).
• Pinho Rui, Helen Crowley, “Revision of eurocode 8 formulae for periods of vibration and their employment in
linear seismic analysis” e. Cosenza (ed), eurocode 8 perspectives from the Italian standpoint workshop, pp- 95-108,
© Doppiavoce, Napoli, Italy. (2009).
• Sangamnerkar Prakash, Dubey S.K. “Comparative study on the static and dynamic behavior of reinforced concrete
framed building”. IOSR journal of mechanical and civil engineering (IOSR-JMCE) ISSN: 2278-1684,p-issn: 2320-334X,
volume 10, issue 4 , pp 01-07. (2013).