The importance of non-spectral intensity measures on the risk-based structural responses

摘要

This study examines the impact of neglecting non-spectral parameters of ground motions (GMs), particularly GM duration, on the structural responses using a risk-based seismic assessment framework, which measures the annual rates of exceedance for a specified amplitude of structural response. This study gives a special attention to the role of the primary intensity measure (IM) that used to characterize the severity of GM (i.e., known as the conditioning IM) on the degree to which GM duration affects the risk-based structural responses. For this purpose, the responses of three steel moment resisting frame buildings are compared when subjected to different ensembles of GMs selected based on the generalized conditional intensity measure (GCIM). The GCIM framework can include different features of GMs in the GM selection process through constructing their conditional distributions given a specified conditioning IM. However, the conditional distributions of GM features change as the conditioning IM changes. The results demonstrate that for all considered conditioning IMs in this study, except spectrum intensity (SI), it is nearly impossible to select a set of as-recorded GMs with the unbiased distributions for all considered IMs, particularly over rare hazard levels. In addition, the results indicate that neglecting non spectral IMs, when the conditioning IM is SI, could overestimate (up to 50% over rare earthquake intensity levels) the MIDR risk-based structural responses with respect to a reference structural response, which resulted from a set of GMs with the unbiased distributions for all considered IMs, for the considered buildings and site. Furthermore, the findings confirm that GM duration in terms of significant duration even in case of shallow events could be an important parameter to be incorporated in GM selection. For the present case study structures and considered site, the induced bias in structural responses due to neglecting GM duration could vary up to about 40% over the rare hazard levels depending on the applied conditioning IM.