Collapse limit state definition for seismic assessment of code-conforming RC buildings

This paper presents a study on the selection of engineering demand parameters (EDPs) for the definition of collapse for code-conforming reinforced concrete buildings. The definition of collapse for buildings is not unique, as different codes and authors define it with respect to different EDPs and different values of the EDPs. Since collapse is associated with large plastic deformations, collapse is typically defined by deformation, displacement, and eventually energy EDPs. The EDPs can be either local when they refer to a single structural element response parameter (such as element rotation with respect to the chord) or global when they refer to an overall building response parameter (such as inter-story drift or top floor displacement). The Italian buildings code NTC2008 and Eurocode 8 use the chord rotation as EDP, while FEMA 356 and other North American literature use inter-story drift ratio. This study compares different definitions of EDPs and different values of the selected EDPs by analyzing two code-conforming benchmark buildings, one six-story and the other nine-story high, designed according to Italian code. Multiple-stripe, non-linear dynamic analyses are carried out on the two buildings modeled with concentrated hinges. The results show that different collapse definitions lead to very different safety evaluations and point to the need for the definition of a single EDP and a single value to make collapse analyses (and risk assessment) studies comparable.