Average spectral acceleration as an intensity measure for collapse risk assessment

Summary This paper investigates the performance of spectral acceleration averaged over a period range ( Sa avg ) as an intensity measure (IM) for estimating the collapse risk of structures subjected to earthquake loading. The performance of Sa avg is evaluated using the following criteria: efficiency, sufficiency, the availability or ease of developing probabilistic seismic hazard information in terms of the IM and the variability of collapse risk estimates produced by the IM. Comparisons are also made between Sa avg and the more traditional IM: spectral acceleration at the first‐mode period of the structure ( Sa(T 1 ) ). Though most previous studies have evaluated IMs using a relatively limited set of structures, this paper considers nearly 700 moment‐resisting frame and shear wall structures of various heights to compare the efficiency and sufficiency of the IMs. The collapse risk estimates produced by Sa avg and Sa(T 1 ) are also compared, and the variability of the risk estimates is evaluated when different ground motion sets are used to assess the structural response. The results of this paper suggest that Sa avg , when computed using an appropriate period range, is generally more efficient, more likely to be sufficient and provides more stable collapse risk estimates than Sa(T 1 ) . Copyright © 2015 John Wiley & Sons, Ltd.