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Validation of Ground-Motion Simulations for Historical Events Using SDoF Systems

Carmine Galasso, Farzin Zareian, Iunio Iervolino, & Robert W. Graves

Published December 2012, SCEC Contribution #1684

The study presented in this paper is among the first in a series of studies toward the engineering validation of Graves and Pitarka’s (2010) hybrid broadband ground motion simulation methodology. This paper provides a statistical comparison between seismic demands of single degree of freedom (SDoF) systems subjected to past events using simulations and actual recordings. A number of SDoF systems are selected, considering: (1) 16 oscillation periods between 0.1s and 6s; (2) elastic case and four nonlinearity levels, from mildly inelastic to severely inelastic systems; and (3) two hysteretic behaviors, namely, non-degrading/non-evolutionary and degrading/evolutionary. Demand spectra are derived in terms of peak and cyclic response, as well as their statistics for four historical earthquakes: 1979 Mw 6.5 Imperial Valley, 1989 Mw 6.8 Loma Prieta, 1992 Mw 7.2 Landers, and 1994 Mw 6.7 Northridge.
This study’s results show that both elastic and inelastic demands to simulated and recorded motions are generally similar. However, for some structural systems, the inelastic response to simulated accelerograms may produce median demands that differ from those obtained using corresponding recorded motions. The magnitude of such differences depends on the SDoF period and the nonlinearity level and, to a lesser extent, on the hysteretic model used. In the case of peak response, these discrepancies are likely due to differences in the spectral shape, while the differences in terms of cyclic response can be explained by some integral parameters of ground motion (i.e., duration-related). Moreover, the intra-event standard deviation values of structural demands calculated from the simulations are generally lower than those given by recorded ground motions, especially at short periods. Assessment of the results using formal statistical hypothesis tests indicates that in most cases the differences found are not significant, increasing the confidence in the use of simulated motions for engineering applications.

Galasso, C., Zareian, F., Iervolino, I., & Graves, R. W. (2012). Validation of Ground-Motion Simulations for Historical Events Using SDoF Systems. Bulletin of the Seismological Society of America, 102(6), 2727–2740. doi: 10.1785/0120120018.