Prediction of inelastic structural response using an average of spectral acceleration

In probabilistic engineering assessment, the ground motion intensity measure (IM), which quantifies the severity of a seismic event, is used both as a scale factor for recorded ground motions in incremental dynamic analysis and as that parameter which defines the seismic hazard at a specified site. In this paper, the geometric mean of pseudo-spectral acceleration ordinates over a certain range of periods, Sa,avg(T1,…,Tn), or briefly Sa,avg, is used as an optimal scalar IM to predict inelastic structural response of buildings subjected to recorded ground motions. This average of spectral values is a better predictor than both the elastic pseudo-spectral acceleration at fundamental period of structure and the peak ground acceleration, 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-values and inelastic IMs. Especially for multi-degree-of-freedom systems with long periods, Sa,avg is very sensitive to higher-mode effects and it is able to account degrading behaviour. Sa,avg is studied as a statistical predictor of structural response through its desirable properties and results are compared with traditional elastic-based scalar IMs.