Conditional Spectrum Based Ground Motion Record Selection Using Average Spectral Acceleration

The use of a seismic intensity measure (IM) is paramount in decoupling seismic hazard and structural response estimation when assessing the performance of structures. For this to be valid, the IM needs to be sufficient, i.e., the engineering demand parameter (EDP) response should be independent of other ground motion characteristics when conditioned on the IM. Whenever non-trivial dependence is found, such as in the case of the IM being the first-mode spectral acceleration, ground motion selection must be employed to generate sets of ground motion records that are consistent vis-à-vis the hazard conditioned on the IM. Conditional spectrum (CS) record selection is such a method for choosing records that are consistent with the site-dependent spectral shape conditioned on the first-mode spectral acceleration. Based on a single structural period, the result may be suboptimal, or insufficient, for EDPs influenced by different period values, e.g., peak interstory drifts or peak floor accelerations at different floors, potentially requiring different record suites for each. Recently, the log-average spectral acceleration over a period range, AvgSA, has emerged as an improved scalar IM for building response estimation whose hazard can be evaluated using existing ground motion prediction equations. Herein, we present a recasting of CS record selection that is based on AvgSA over a period range as the conditioning IM. This procedure ensures increased efficiency and sufficiency in simultaneously estimating multiple EDPs by means of a single IM.