Spectral shape metrics and structural collapse potential

This paper examines various parameters that provide a measure of spectral shape and studies how they relate to the potential of ground motion records to cause the collapse of a given structure. It is shown that when measuring the ground motion intensity by the spectral acceleration at the first-mode period of the structure, Sa(T-1), records causing collapse at low ground motion intensities typically have significantly different spectral shapes than those that do not cause collapse until much higher ground motion intensities. A spectral shape typical of damaging records is identified, and a metric for quantifying the spectral shape of a record called SaRatio is proposed and evaluated. SaRatio is defined as the ratio between Sa(T-1) and the average spectral value over a period range. The ability of SaRatio to predict the collapse intensity, i.e. the minimum intensity at which a given ground motion causes the collapse of a given structure, is compared to other recently proposed spectral shape metrics including epsilon (epsilon), eta (eta) and Np. The results demonstrate that SaRatio is typically a much better predictor of collapse intensity than other spectral shape metrics. Copyright (C) 2016 John Wiley & Sons, Ltd.