Pushover Analysis

PUSHOVER ANALYSIS OF REINFORCED CONCRETE FRAME STRUCTURES


A Synopsis Submitted For

M-Tech In Civil (Structural Engineering)

Under The Faculty Of Engineering

By

Mr. Jadhav Digambar J.

Guide

Dr. A. B. Kulkarni

Applied Mechanics Department

Walchand College of Engineering, Sangli

2012-2013

SYNOPSIS

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Name of College: - Walchand college of Engineering, Sangli

Name of Department: - Applied Mechanics Department

Name of Course: - M.TECH (Civil-Structures)

Name of student: - Mr. Jadhav Digambar J.

Title of Dissertation: - Pushover analysis of reinforced concrete frame structures

Name of Guide: - Dr. A. B. Kulkarni

Relevance: -

The recent earthquakes in which many concrete structures have been severely damaged or collapsed, have indicated the need for evaluating the seismic adequacy of existing buildings. In particular, the seismic rehabilitation of older concrete structures in high seismicity areas is a matter of growing concern, since structures 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. Thus, the structural engineering community has developed a new generation of design and seismic procedures that incorporate performance based structures and is moving away from simplified linear elastic methods and towards a more non linear technique. Recent interests in the development of performance based codes for the design or rehabilitation of buildings in seismic active areas show that an inelastic procedure commonly referred to as the pushover analysis is a viable method to assess damage vulnerability of buildings.

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. The extent of damage experienced by the structure at this target displacement is considered representative of the damage experienced by the building when subjected to design level ground shaking. Many methods were presented to apply the nonlinear static pushover (NSP) to structures. These methods can be listed as: (1) the capacity spectrum method (CSM) (ATC), (2) the displacement coefficient method (DCM) (FEMA), (3) modal pushover analysis (MPA). The approach has been developed by many researchers with minor variation in computation procedure. Since the behavior of reinforced concrete structures may be highly inelastic under seismic loads, the global inelastic performance of RC structures will be dominated by plastic yielding effects and consequently the accuracy of the pushover analysis will be influenced by the ability of the analytical models to capture these effects. In general, analytical models for the pushover analysis of frame structures may be divided into two main types: (1) distributed plasticity (plastic zone) and (2) concentrated plasticity (plastic hinge).

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Although the plastic hinge approach is simpler than the plastic zone, this method is limited to its incapacity to capture the more complex member behavior that involve severe yielding under the combined actions of compression and bi-axial bending and buckling effects.

Literature review:-

Following are some literature and references from which the objectives of this dissertation work have been decided.

A. Vijaykumar and D. L. Venkatesh Babu (2012) [1]aims to evaluate the zone III selected existing reinforced concrete building to conduct the non-linear static analysis (Pushover Analysis). The pushover analysis shows the pushover curves, capacity spectrum, plastic hinges and performance level of the existing building. They also evaluate the behaviour of G+2 reinforced concrete bare frame subjected to earthquake forces in zone III. The reinforced concrete structures are analyzed by nonlinear static analysis (Pushover Analysis) using SAP2000 software. It shows the performance levels, behaviour of the components and failure mechanism in a building. It also shows the types of hinge formation. The strength and capacity of the weakest components are then increased by retrofitting techniques. The non-linear static analysis gives better understanding and more accurate seismic performance of buildings as progression of damage or failure can be traced.

P. Poluraju and P. V. S. Nageswara Rao (2011) [2]evaluate the performance of framed buildings under future expected earthquakes, a non-linear static pushover analysis has been conducted. To achieve this objective, G+3 building was analysed using the software Sap2000. The results of pushover analysis of reinforced concrete frames designed according to the IS1893:2002. The Results of this paper was explained in terms of pushover curve, capacity-demand curve and in terms of plastic hinges. The result shows that properly designed frame will perform well under seismic loads.

A. Kadid and A. Boumrkik (2008) [3] study the comparison the performance of framed buildings under future expected earthquakes, a non linear static pushover analysis has been conducted. To achieve this objective, three framed buildings with 5, 8 and 12 stories respectively were analyzed by using the software SAP2000. The Results of this paper was explained in terms of pushover curve, capacity-demand curve and in terms of plastic hinges. The results show that the comparison of three buildings corresponding to capacity-demand curves and their plastic hinge formation. The results obtained from this study show that properly designed frames will perform well under seismic loads.

A. K. Chopra and R. K. Goel (2001) [4] study investigation is to develop a pushover analysis procedure based on structural dynamics theory, which retains the conceptual simplicity and computational attractiveness of current procedures with invariant force distribution, but provides superior accuracy in estimating seismic demands on buildings. For that 9-story building is analysed using the force distribution methods in FEMA and Modal Pushover Analysis (MPA)

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method. The comparison of result was also shows in this paper. The results are show that the MPA method is more accurate than the force distribution in FEMA.

Peter Fajfar (2000) [5] studies the relatively simple Non-linear method for seismic analysis of structure (N2 method). The method is described and discussed, and its basic derivations are given. The similarities and differences between the proposed method and FEMA 273 and ATC 40 are discussed. For that the four story building is analyzed using these three methods. The results shows that the proposed Method gives accurate result than other two methods.

Objectives:-

In this work pushover analysis is used. An incremental displacement approach is used. A

pushover procedure is applied to following-

a) A framed structure designed as per IS 456-2000, without any provision for seismic

resistance.

b) A framed structure designed as per IS 456-2000 and also as per IS 1893-2001.

The pushover analysis is used to assess the performance of these building as per FEMA

specification. The method is further used is suggest retrofitting in seismic deficient structure.

Facilities Available:-

Computer lab: - Applied Mechanics Department, WCE, Sangli

Central Computer Facility:-WCE, Sangli

Library:-WCE, Sangli

Expected date of completion: - 30th June 2013

Approximate Cost- Rs.7000/-

Jadhav Digambar J. Dr. A. B. Kulkarni

(Student) (Guide)

Dr. S. N. Tande

(H.O.D.)

Applied Mechanics Dept.

W.C.E. Sangli

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References:-

1) A. Vijaykumar and D. L. Venkatesh Babu (2012) ,‘Pushover analysis of existing reinforced concrete framed structures’, European Journal of Scientific Research, vol.71, No.2, pp. 195-202.

2) P. Poluraju and P. V. S. Nageswara Rao (2011), ‘Pushover analysis of reinforced concrete Frame structures using SAP2000’, International Journal of Earth Sciences and Engineering, Vol.04, No.06 SPL, pp. 684-690

3) Kadid, A., and Boumrkik, A. (2008), ‘Pushover analysis of reinforced concrete framestructures’, Asian Journal of Civil Engineering (building and housing), 9, pp.75-83.

4) Chopra A.K., Goel R.K. (2001), ‘A modal pushover analysis procedure to estimate seismic demands for buildings: Theory and preliminary evaluation’, Pacific Earthquake Engineering Research Centre, Report No. PEER 2001/03, University of California, Berkeley, California.

5) Fajfar P. (2000), ‘A Non- linear analysis method for performance based seismic design’, Earthquake Spectra, Vol.16, No.3, pp. 573-592.

6) FEMA, (1997), NEHRP – Guidelines for the Seismic rehabilitation of buildings, FEMA 273, NEHRP – Commentary on the guidelines for the seismic rehabilitation of buildings, FEMA 274, Federal Emergency Management Agency Washington. D.C. Federal Emergency Federal Agency, FEMA-356.Prestandard and Commentary for Seismic Rehabilitation of Buildings. Washington DC, 2000.

7) ATC 40, (1996), Seismic evaluation and retrofit of concrete buildings Applied Technology Council.

8) IS: 456, (2000), Plain and Reinforced Concrete- code of Practice, Bureau of Indian standards, India

9) IS: 1893 (Part I), (2002), Criteria for earthquake resistant design of structures (Fifth Revision) Indian Standards, New Delhi.

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Pushover Analysis