Evaluation of the Adjustment of the Collapse Capacity by Epsilon in the FEMA P‐695 Methodology

ABSTRACT The FEMA P‐695 document proposed a methodology to evaluate if a structure meets an acceptable probability of collapse at the MCE. It includes a modification of the median collapse capacity to account for differences in the spectral shape of ground motions expected at a site at the target hazard level of interest to that of the records used in the analyses. This modification is done as a function of the parameter epsilon, defined as the number of standard deviations by which the spectral acceleration ordinate computed from a record differs from that estimated by a ground motion model. This study evaluates this adjustment by using seven moment‐resisting frame buildings when subjected to 269 recorded ground motions. Consistent with previous studies, ground motion intensities triggering collapse exhibit an increasing trend as epsilon increases. By using Next‐Generation Intensity Measures, it is shown that this trend is primarily produced by characteristics of the ground motions other than epsilon. Results indicate that once these are accounted for by using intensity measures that are better correlated with collapse, the effects of epsilon on collapse capacity are small. Therefore, it is concluded that the collapse capacity adjustment currently proposed in the FEMA P695 methodology is not recommended.