Spectral shape proxies and nonlinear structural response

In this paper, spectral-shape-based intensity measures (IMs) are discussed with respect to ordinary, pulse-like and narrow-band records. First, the analyses address the ability of these IMs to capture the peak and cumulative damage potentials of ground motions. Second, a new vector-valued ground motion IM based on the spectral acceleration at the first mode of the structure, Sa(T-1), and a parameter proxy for the spectral shape, namely N-p, is introduced. The vector <Sa,N-p> is compared to other state-of-the-art IMs in terms of estimation of the seismic response of nonlinear single degree of freedom systems, reinforced concrete and steel moment resisting frames. Results show that <Sa,N-p> may be especially useful to represent the ground motion potential in the case of records with peculiar spectral shape. Further, it is shown that <Sa,N-p> has the properties of efficiency, sufficiency and scaling robustness. Finally, a scalar ground motion IM based on Sa(T-1) and N-p is also discussed, and the possibility to compute the seismic hazard analysis for it is illustrated. (C) 2011 Elsevier Ltd. All rights reserved.