New scalar intensity measure for near-fault ground motions based on the optimal combination of spectral responses

Intensity Measure (IM), characterizing the strength of an earthquake ground motion, is used to predict the seismic responses of a structure. Recent studies have demonstrated that using Sa(T1)Sa(T1) as the seismic scaling index for near-fault ground motions may introduce large variability in the estimated seismic demands. To develop an improved IM, this paper investigates the effectiveness of a large number of combinations of spectral values in reducing scatter in the estimated maximum interstorey drift ratios. For this purpose, Incremental Dynamic Analyses (IDAs) are performed for five generic frames of short-to-relatively long periods, under 40 pulse-like earthquake records. Statistical evaluation of the IDA results reveals that the optimal combination of spectral displacements, compared to that of spectral velocities, leads to less variability for all ranges of the frames. It is concluded that the optimal combination of spectral displacements can be used to predict seismic demands with dispersions less than those of Sa(T1)Sa(T1), and which are closer to constant for various intensity levels. Additionally, with respect to the importance of collapse capacity predictions in earthquake engineering, an efficient IM that can considerably improve the accuracy of estimating the probability of collapse is also developed.