SEISMIC RESPONSE OF EXISTING RC BUILDING UNDER REVISED SEISMIC ZONE CLASSIFICATION USING PUSHOVER ANALYSIS

Seismic Response of Existing RC Building Under Revised Seismic Zone Classification Using Pushover
Analysis, V.Panneer Selvam, K.Nagamani , Journal Impact Factor (2015): 9.1215 (Calculated by GISI)
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www.iaeme.com/ijciet.asp 23 editor@iaeme.com
#
Research Scholar, College of Engineering, Anna University, Chennai
*
Professor, College of Engineering, Anna University, Chennai
ABSTRACT
Existing Reinforced Concrete (RC) buildings constructed before two decades typically have
the design details which are considered to be highly inadequate under the present revised seismic
code of practice. Many of these structures have suffered significant structural damage during recent
earthquakes. Significant research effort has been devoted to the development of behavioral models
and modeling techniques to predict the behavior of these buildings. However there are no models
that have been shown to predict observed response with a high level of accuracy and precision. In
this paper, a seven storey RC building is considered to investigate the structural seismic response.
This RC building is analysed and designed for the gravity and lateral loads using the codal
provisions followed a decade ago (previous version of the code). Then the designed structure is
evaluated for the seismic performance under the old and the revised code of practice using Pushover
Analysis. The Displacement controlled Pushover Analysis was carried out and the Pushover Curve
was obtained for the building in both X and Y directions. The Capacity Spectrum, Demand Spectrum
and Performance point of the building, under old and the revised seismic zone classification was
found in both the direction using the analysis carried out in SAP 2000. From the analysis it is
understood that, the frame is capable of withstanding the presumed seismic force with some
significant yielding at several beams. The results obtained in terms of demand, capacity and plastic
hinges gave an insight into the real behaviour of structure.
Keywords: Pushover Analysis, Old RC Building, Capacity Curve, Performance Point, Plastic Hinge.
1.0 INTRODUCTION
The recent earthquakes in India have led to an increase in the seismic zoning factor over
many parts of the country. Also, ductility has become an issue for all those buildings that were
designed and detailed using earlier versions of the codes. Many concrete structures have been
collapsed or severely damaged during these earthquakes. This indicates the need for evaluating the
seismic adequacy of existing buildings. India’s four recent upgraded seismic zones emphasize this
for more than 60% of the land. Under such circumstances, seismic qualification of existing buildings
under revised codes has become extremely important. In particular, the seismic rehabilitation of
older concrete structures in high seismicity areas is a matter of growing concern, since structures
SEISMIC RESPONSE OF EXISTING RC BUILDING UNDER REVISED
SEISMIC ZONE CLASSIFICATION USING PUSHOVER ANALYSIS
V.Panneer Selvam#
, K.Nagamani*
Volume 6, Issue 6, June (2015), Pp. 23-32
Article Id: 20320150606003
International Journal of Civil Engineering and Technology (IJCIET)
© IAEME: www.iaeme.com/Ijciet.asp
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
IJCIET
© I A E M E

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venerable to damage must be identified and an acceptable level of safety must be determined. To
make such assessment, simplified linear-elastic methods are not adequate. One of the emerging fields
in seismic design of structures is the Performance Based Design. Nonlinear static analysis or push
over analysis has been developed over the past years and has been a preferred procedure for seismic
performance evaluation of several structures. Basically, a pushover analysis is a series of incremental
static analysis carried out to develop a capacity curve for the building. Based on the capacity curve, a
target displacement which is an estimate of the displacement that the design earthquake will produce
on the building is determined.
Peter Fajfar and M.Eeri [1] carried out studies on a nonlinear analysis method for
performance based seismic design. In this paper, the author has presented a simple non linear method
for seismic analysis of structures. It combines the push over analysis of multi degree of freedom
model with response spectrum analysis of an equal single degree of freedom system. The method is
formulated in acceleration-displacement format, which enables the visual interpretation of the
procedure and of relations between basic quantities controlling seismic response. Inelastic spectra,
rather than elastic spectra with equivalent damping and period are applied. This feature represents
the major difference with respect to the capacity spectrum method. Moreover demand quantities are
obtained without iterations. Generally, the results of the N2 method are reasonably accurate,
provided that the structure oscillates predominantly in the first mode. Some additional limitations
apply. M. Seifi, J. Noorzaei, M. S. Jaafar, E. YazdanPanah [2] presents the state of the art
development in nonlinear static pushover analysis in earthquake engineering. In this paper, the
authors compared nonlinear static pushover (NSP) analysis to nonlinear dynamic time-history
analysis. Conceptually, NSP method relies on pushing the structure with incremental static lateral
load by considering material inelasticity and geometric nonlinearity. Pushover procedure for
evaluating the seismic adequacy of reinforced concrete frames was presented by A. Shuraim, A.
Charif [3]. In this paper the author has utilized nonlinear static analytical procedure (Pushover) as
introduced by ATC-40 for the evaluation of existing design of a reinforced concrete frame, in order
to examine the applicability of the pushover for evaluating design of new buildings. In the first
approach, the potential deficiencies were determined by redesigning under one selected seismic
combination in order to show which members would require additional reinforcement. In the second
approach, a pushover analysis was conducted to assess the seismic performance of the frame and
detect the locations of the plastic hinges. The paper shows that vulnerability locations revealed from
the two procedures are significantly different, where the latter procedure tends to overestimate
column strength, consequently, concealing earlier detection of column weaknesses. The paper
provides rational explanations for the apparent discrepancy that can be taken into consideration in
order to make pushover methodology applicable when designing or evaluating existing design of
new buildings. Rahul Rana, Limin Jin and AtilaZekioglu [4] carried out push over analysis of a 19
storey concrete shear wall building”.In this paper, author has done Pushover analysis on a nineteen
story, slender concrete tower building located in San Francisco with a gross area of 430,000 square
feet. NieJiaguo, Qin Kai, Xiao Yan [5] carried out studies on push-over analysis of the seismic
behavior of a concrete-filled rectangular tubular frame structure. In this paper, in order to investigate
the seismic behavior of concrete-filled rectangular steel tube (CFRT) structures, push-over analysis
of a 10-story moment resisting frame (MRF) composed of CFRT columns and steel beams was
conducted. The results show that push-over analysis is sensitive to the lateral load patterns, so the
use of at least two load patterns that are expected to bound the inertia force distributions is
recommended. Oguz, Sermin [6] carried out evaluation of pushover analysis procedures for frame
structures. Modal Pushover Analysis on reinforced concrete and steel moment resisting frames
covering a broad range of fundamental periods was carried out. Certain response parameters
predicted by each pushover procedure were compared with the 'exact' results obtained from

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nonlinear dynamic analysis. A. Ismail [7] carried out non linear static analysis of a retrofitted
reinforced concrete building. In this study, the author made an attempt for investigating the seismic
behavior of a typical existing building in Cairo by performing static pushover analysis before and
after retrofitting the columns by reinforced concrete, steel sections or carbon fiber reinforced
polymer (CFRP) composite jackets.
In this paper the author has carried out pushover analysis for evaluation of seismic
performance of existing reinforced concrete structure under revised seismic zone classification. The
present study is to evaluate the behavior of existing seven storey reinforced concrete structure
located in Chennai region, which was designed as per the earlier version of the seismic code (IS:
1893 – 1984), to comply with the provision mentioned in the revised version of seismic code (IS
1893 (Part 1) : 2002).
2.0 PUSHOVER ANALYSIS
Pushover analysis (Fig. 1) is a nonlinear static analysis for a reinforced concrete (RC) framed
structure subjected to lateral loading.This lateral loads represents the inertial forces which the
structure would be experienced when subjected to ground shaking.First gravity loads are applied, and
then the lateral load is applied incrementally at the end of the gravity push. Building is displaced till
the ‘control node’ reaches ‘target displacement’ or building collapses.The sequence of cracking,
plastic hinging and failure of the structural components throughout the procedure is observed.Using
a pushover analysis, a characteristic non linear force-displacement relationship (Base shear & control
node displacement) can be determined.
Pushover analysis is a static, nonlinear procedure in which the magnitude of the lateral force
is incrementally increased, maintaining the predefined distribution pattern along the height of the
building. Pushover analysis can determine the strength (weak links and failure modes), and drift
capacity and the seismic demand for this structure subjected to selected earthquake. Local Nonlinear
effects are modeled and the structure is pushed until a collapse mechanism gets developed. At each
step, the base shear and the roof displacement can be plotted to generate the pushover curve. It gives
an idea of the maximum base shear that the structure was capable of resisting at the time of the
earthquake. For regular buildings, it can also give a rough idea about the global stiffness of the
building. The responses obtained from pushover analysis are:

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Fig. 1 Schematic Representation of Pushover Analysis Procedure
Estimates of force and displacement capacities of the structure.
Estimates of force (axial, shear and moment) demands on potentially brittle elements and
deformation demands on ductile elements.
Estimates of global displacement demand, corresponding inter-storey drifts and damages on
structural and non-structural elements expected under the earthquake ground motion considered.
Sequences of the failure of elements and the consequent effect on the overall structural
stability.
Identification of the critical regions, where the inelastic deformations are expected to be high
and identification of strength irregularities (in plan or in elevation) of the building.
In pushover analysis the building is pushed with a specific load distribution pattern along the height
of the building. The magnitude of the total force is increased but the pattern of the loading remains
same till the end of the process. Pushover analysis results (i.e., pushover curve, sequence of member
yielding, building capacity and seismic demand) are very sensitive to the load pattern. The lateral
load patterns should approximate the inertial forces expected in the building during an earthquake.
The distribution of lateral inertial forces determines relative magnitudes of shears, moments, and
deformations within the structure. The building has to be modeled to carry out nonlinear static
pushover analysis. This requires the development of the force - deformation curve for the critical
sections of beams, columns. The force deformation curves in flexure were obtained from the
reinforcement details and were assigned for all the beams and columns.User-defined PMM (PM-M
hinges are assigned at the ends of column members which are subjected to axial force and bending
moments) and M3 (M3 hinges are assigned at the ends of beam members which are subjected to
bending moments) curves are developed using the rotation capacities of members. Target
displacement is the displacement demand for the building at the control node subjected to the ground
motion under consideration. This is a very important parameter in pushover analysis because the
global and component responses (forces and displacement) of the building at the target displacement
are compared with the desired performance limit state to know the building performance. There are
two approaches to calculate target displacement: Displacement Coefficient Method (DCM) of FEMA
356 and Capacity Spectrum Method (CSM) of ATC 40. Both of these approaches use pushover
curve to calculate global displacement demand on the building from the response of an equivalent
single-degree-of-freedom (SDOF) system.

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3.0 DESCRIPTION OF THE FRAMED STRUCTURE
A residential building having stilt + 6 floors located in Chennai (Fig. 2) is considered for the
analysis. Each floor contains 6 apartments (total 48 apartments). The building was analysed and
designed for the combination of Dead, Live, Wind and Seismic load. The seismic analysis of the
building was carried out using IS: 1893 – 1984. Geometrical details are,
Length – 42.7m
Width – 18.3m
Height – 21.2m
Dead load due to brick wall, finishes, beam, column & slab are calculated based on the unit
weight of material. Brick load are calculated for height of wall. Live load on floor is 2 kN/m2
& on
Roof is 1.5 kN/m2
. Wind load on the building is calculated as per IS 875 (Part-III).
Seismic load is calculated as per IS: 1893 – 1984.
Seismic Zone = 2
Basic horizontal seismic coeff., αo = 0.02 αh = β I αo
Coefficient, β = 1
Importance Factor, I = 1
Design Hor. Seismic Co-efficient, αh = 0.02 (αh= β I αo)
Time period = 0.47 s (x-dir) & 0.30 s (y-dir)
Co-eff based on flexibility, C = 0.7 (x-dir) & 1.0 (y-dir)
Design Base Shear, Vb = 0.014W (x-dir) & 0.02W (y-dir)
Seismic load is calculated as per IS: 1893 (Part 1) – 2002.
Seismic Zone = 2
Seismic Intensity = 0.1
Importance Factor = 1
Response Reduction Factor = 3
Time period = 0.47 s (x-Dir)
= 0.30 s (y-dir)
Spectral Acceleration, Sa/g = 2.5 (both x & y -Dir)
Design Hor. Seismic Co-efficient = 0.04167
Design Base Shear, Vb = 0.04167W
Seismic load is calculated as per IS: 1893 (Part 1) – 2002.
Seismic Zone = 3
Seismic Intensity = 0.16
Importance Factor = 1
Response Reduction Factor = 3
Time period = 0.47 s (x-Dir)
= 0.30 s (y-dir)
Spectral Acceleration, Sa/g = 2.5 (both x & y -Dir)
Design Hor. Seismic Co-efficient = 0.0667
Design Base Shear, Vb = 0.0667W
Where, W = total dead load + appropriate amount of live load

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Fig. 2 3D View of the Existing Reinforced Building
The pushover analysis of the building is carried out in SAP. Initially the basic model of the
building is created in SAP as shown in Fig. 3.
Fig. 3 3D Building Model created in SAP
The properties and acceptance criteria for the pushover hinges are defined for the model.
Several built-in default hinge properties are available for concrete and steel in SAP. Then the
pushover hinges are located in the model by selecting one or more frame members and assigning
them hinge properties. The pushover load cases are defined in the software. First basic static analysis
and dynamic analysis are carried out on the model. Then static non linear pushover analysis is
carried out. The capacity curve of the building along x direction is shown in Fig. 4. The plastic hinge
pattern in the building along one typical duirection (x direction) is given in Table 1.
Fig. 4 Capacity Curve of the Building

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The performance levels are the discrete damage states identified from a continuous spectrum
of possible damage states (Fig. 5). The structural performance levels based on the roof drifts are
labeled as A, B, C, D and E are used to define the force deflection behavior of the hinge. The
performance levels (IO, LS, and CP) of a structural element are represented in the load versus
deformation curve as shown below,
1) A to B – Elastic state,
i) Point ‘A’ corresponds to the unloaded condition.
ii) Point ‘B’ corresponds to the onset of yielding.
2) B to IO- below immediate occupancy,
3) IO to LS – between immediate occupancy & life safety,
4) LS to CP- between life safety to collapse prevention,
5) CP to C – between collapse prevention and ultimate capacity,
i) Point ‘C’ corresponds to the ultimate strength
6) C to D- between C and residual strength,
i) Point ‘D’ corresponds to the residual strength
7) D to E- between D and collapse
i) Point ‘E’ corresponds to the collapse.
Fig. 5 Performance Level of a Structure
Table 1 Plastic hinge pattern for X Direction
The capacity spectrum of structure obtained for x direction for zone II and Zone III is shown
in Fig.6a and 6b. The plastic hinge pattern for the building is shown in Fig. 7a & 7b.

Seismic Response of Existing RC Building Under Revised Seismic Zone Classification Using
Analysis, V.Panneer Selvam, K.Nagamani
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Table 1b
The capacity spectrum of structure obtained for x direction for zone II and Zone III is shown
in Fig.6a and 6b. The plastic hinge pattern for the building is shown in Fig. 7a & 7b.
Fig. 6a
Fig. 6b
Seismic Response of Existing RC Building Under Revised Seismic Zone Classification Using
V.Panneer Selvam, K.Nagamani , Journal Impact Factor (2015): 9.1215 (Calculated
30
Table 1b Plastic hinge pattern for Y Direction
capacity spectrum of structure obtained for x direction for zone II and Zone III is shown
inge pattern for the building is shown in Fig. 7a & 7b.
Fig. 6a Capacity Spectrum for Zone II
Fig. 6b Capacity Spectrum for Zone III
, Journal Impact Factor (2015): 9.1215 (Calculated by GISI)
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capacity spectrum of structure obtained for x direction for zone II and Zone III is shown
inge pattern for the building is shown in Fig. 7a & 7b.

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Fig. 7a Plastic Hinge Formation X Direction
Fig. 7b Plastic Hinge Formation Y Direction
4.0 SUMMARY AND DISCUSSIONS
The existing, 12 year old, 6-storey residential building located in Chennai is analyzed and
designed for different combinations of dead, live, wind and seismic code provisions. After
construction, the seismic code WAS revised with upgradation of seismic zones over many parts of
the country. Hence the qualification of the existing structure under the revised seismic zone has to be
studied. The nonlinear static analysis (pushover analysis) is a relatively simple way to explore the
nonlinear behaviour of buildings. Analytical model was created, representing the existing building,
using elastic beam and column members as elastic elements with plastic hinges at their ends.
Analytical models are incorporated to represent inelastic material behaviour and inelastic member
deformations for simulating numerically the post yield behaviour of the structure under expected
seismic load. Pushover analysis is performed on the existing building for both zones (II & III).
Target displacement of the building was 80 mm but the building is analysed for the displacement
upto 200 mm. Pushover parameters were evaluated and compared for both zones.
5.0 CONCLUSIONS
From the analysis it is understood that, the frame is capable of withstanding the presumed
seismic force with some significant yielding at several beams. The results obtained in terms of
demand, capacity and plastic hinges gave an insight into the real behaviour of structure. All the
plastic hinges formed in the beams, columns are within the acceptance criteria of plastic hinge.
Lateral deformations at the performance point are within the target displacement of the structure.
Maximum total drift, maximum inelastic drift, and structural stability does not exceed the limitations
of the performance level, therefore the present building is considered safe against the revised seismic
provisions.

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REFERENCES
1. Peter Fajfar, Eeri, M (2000); “A nonlinear analysis method for performance based seismic
design”. Earthquake spectra, vol.16, no: 3, pp-573 to 592.
2. M. Seifi, J. Noorzaei, M. S. Jaafar, E. YazdanPanah (2008); “Nonlinear Static Pushover
Analysis in Earthquake Engineering: State of Development”.ICCBT2008.
3. A. Shuraim, A. Charif;”Performance of pushover procedure in evaluating the seismic adequacy
of reinforced concrete frames”. King Saud University.
4. Rahul RANA, Limin JIN and Atila ZEKIOGLU (2004); “Push over analysis of a 19 story
concrete shear wall building”.13th World Conference on Earthquake Engineering Vancouver,
B.C., Canada August 1-6, 2004 Paper No. 133.
5. NIE Jiaguo, QIN Kai, XIAO Yan (2006); “Push-Over Analysis of the Seismic Behavior of a
Concrete-Filled Rectangular Tubular Frame Structure”. TSINGHUA SCIENCE AND
TECHNOLOGY ISSN 1007-0214 20/21 pp124-130, Volume 11, Number 1, February 2006.
6. Oğuz, Sermin(2005); “Evaluation of pushover analysis procedures for frame structures”..
Graduate School of Natural and Applied Sciences.
7. A. Ismail (2014) “Non linear static analysis of a retrofitted reinforced concrete building”
HBRC Journal (2014) 10, 100–107.
8. Dr. Suchita Hirde and Ms. Dhanshri Bhoite, “Effect of Modeling of Infill Walls on
Performance of Multi Story RC Building” International Journal of Civil Engineering &
Technology (IJCIET), Volume 4, Issue 4, 2013, pp. 243 - 250, ISSN Print: 0976 – 6308, ISSN
Online: 0976 – 6316.
9. Turkia Haithem and Lahbari Noureddine, “Seismic Response Model Including SSI of RC
Buildings on Isolated and Raft Foundations” International Journal of Civil Engineering &
Technology (IJCIET), Volume 6, Issue 3, 2015, pp. 118 - 131, ISSN Print: 0976 – 6308, ISSN
Online: 0976 – 6316.
10. Shaikh Zahoor Khalid & S.B. Shinde, “Seismic Response of FRP Strengthened RC Frame”
International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012,
pp. 305 - 321, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

SEISMIC RESPONSE OF EXISTING RC BUILDING UNDER REVISED SEISMIC ZONE CLASSIFICATION USING PUSHOVER ANALYSIS

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SEISMIC RESPONSE OF EXISTING RC BUILDING UNDER REVISED SEISMIC ZONE CLASSIFICATION USING PUSHOVER ANALYSIS