Determining the seismic performance factors of quasi-X bracing systems

Abstract

This paper proposes two novel quasi-X bracing systems to resolve the drawbacks of concentrically braced frames (CBFs) and enhance their ductility. The seismic performance factors (SPFs) for moment-resisting frames equipped with these braces are determined according to the FEMA P695 approach. In pursuit of this aim, a three-dimensional set of 2-, 4-, 6-, and 8-story archetypes in two separate seismic design categories (SDC Cmax and Cmin) were designed considering presumed SPFs. Initially, non-linear static (pushover) analysis was carried out on each of the archetypes, and their period-based ductility and over-strength factors were extracted. Afterward, the archetypes' seismic performance was evaluated by performing incremental dynamic analysis (IDA) under far-field ground motion (FFGM) records, and the accuracy of the presumed response modification factor was examined as per FEMA P695. Based on the obtained results, a response modification factor of 5 is deemed acceptable for the design of both quasi-X bracing systems. Furthermore, the values of the deflection amplification factor and the over-strength factor are acquired as 5 and 3, respectively.