Improved scalar intensity measures in performance-based earthquake engineering

Abstract

An earthquake intensity measure (IM) is a characteristic of a recorded ground motion that quanti…es the severity of a seismic event. In reliability analysis of structural systems subjected to ground shaking, the choice of IM plays a leading role. In probabilistic engineering assessment, the IM is used both as a scale factor for recorded ground motions in incremental dynamic analysis and as that parameter which de…nes the seismic hazard at a speci…ed site. In this paper, the geometric mean of pseudo-spectral acceleration ordinates over a certain range of periods, Sa,avg, is used as a scalar IM to predict inelastic structural response of buildings subjected to recorded ground motions. This average of spectral values is a better predictor than the elastic pseudo-spectral acceleration at fundamental period of structure, Sa, especially for inelastic structural systems. Furthermore, the seismic hazard at the site in terms of Sa,avg as IM is simpler than the one performed for vector-valued and inelastic IMs. Especially for inelastic multi-degree-of-freedom systems with long periods, Sa,avg is very sensitive to higher-mode effects, showing a limited levels of dispersion at different given ductility levels. Sa,avg is studied as a statistical predictor of structural response and is compared with conventional elastic and inelastic scalar IMs. The study is completed with suggestions about the period range over which the average should be calculated, the spacing periods and the necessary number of points of spectral ordinates, in order for Sa,avg to be most effective.