An approximate procedure for estimating seismic demands for buildings

Benazouz Chikh,Youcef Mehani,Mohamed Hadid,Moussa Leblouba,A Shanableh,M Omar,S Al-Toubat,R Al-Ruzouq,K Hamad,S Barakat,M Maalej

doi:10.1051/matecconf/201712001002

Abstract

Methods of the estimation of the seismic demands of nonlinear structures require a sort of iterative procedures, no matter the elastic or inelastic response spectra are used in the procedure. Many studies dealt with the development of different inelastic spectra with the aim to simplify the evaluation of inelastic deformations and performance of structures. Recently, the concept of inelastic spectra has been adopted in the global scheme of the performance-based seismic design through capacity-spectrum methods (CSM). For instance, the modal pushover analysis (MPA) has been proved to provide accurate results for inelastic buildings to a similar degree of accuracy to the response spectrum analysis (RSA) in estimating peak response for elastic buildings. In this paper, a simplified nonlinear spectral analysis is made to the original MPA is proposed. The proposed procedure, which is applicable to multi-degree-of-freedom MDOF systems uses an inelastic spectrum and gives peak responses consistent with those obtained when using the nonlinear time history analysis (NL-RHA). The accuracy of the proposed procedure is verified against the nonlinear time history analysis results of two buildings. The comparison showed that the new method is capable to provide accurate peak response.

Highlights

For convenience we summarize the modal pushover analysis (MPA) as a series of steps used to estimate the peak inelastic response of MDOF (Chopra 2007): 1. Compute the natural frequencies, ߱௡ and modes, ߶௡, for linearly elastic vibration of the building
The construction of the capacity curve starts with obtaining the multimodal pushover curves of the MDOF system subjected to lateral forces distributed over the building height according to ܵ௡‫כ‬, where the movements will be decomposed in the form of a series of normal modes
An approximate procedure for seismic demands assessment of MDOF system has been developed and its accuracy was verified by examples

Summary

Introduction

As an alternative to the complex nonlinear dynamic analysis to estimate the seismic demands of structures, several simple evaluation methods have been proposed (Gulkan and Sozen 1974; Freeman 1975; Newmark and Hall 1982; Fajfar and Fischinger 1988; Kowalsky 1994; Sasaki et al 1998; Gupta and Kunnath 2000; Albanesi et al 2000; Priestley and Kowalsky 2000; Miranda 2001; Chopra and Goel 2001; Lin and Chang 2003; Maja and Fajfar 2012; Benazouz et al 2012) Such methods are based on the characterization of the structural capacity and the good quantification of seismic intensity, such as the Capacity Spectrum Method CSM (Freeman 1975) and its different implementations. Fajfar (1999) have proposed a N2 method for nonlinear analysis of seismic damage of reinforced concrete buildings This method employs an inelastic response spectrum and the capacity curve is obtained from a single-degree-of-freedomsystem (SDOF) equivalent to the multi-degree-of-freedom-system (MDOF). It is implemented in Eurocode 8 (CEN 2005) and it was used in a comparison between traditional non-linear static methods in the evaluation of asymmetric structures

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Methods

Discussion

Conclusion