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(T1), and a parameter proxy for the spectral shape, namely Np, is introduced. The vector 〈Sa,Np〉 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,Np〉 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,Np〉 has the properties of efficiency, sufficiency and scaling robustness. Finally, a scalar ground motion IM based on Sa(T1) and Np is also discussed, and the possibility to compute the seismic hazard analysis for it is illustrated.