Evaluating seismic response modification factor of steel frames with different bracing systems

Abstract

This paper aims to evaluate seismic response modification factor, overall ductility factor, and overstrength factor of ordinary moment steel frames with different concentrically bracing systems (X-bracing, V-bracing, and inverted V-bracing). The effects of bracing type and number of stories have been considered in the course of this study. Such factors effects on seismic parameters are not considered in seismic codes such as International Building Code (IBC, 2012) and European Standards (EN). Linear time history analysis has been performed using multiple earthquake records selected to include the variability in ground motion characteristics for 4-, 8-, 12-, and 16-story steel frame buildings. Nonlinear pushover analysis was then carried out by assigning nonlinear material behaviour and plastic hinges to steel elements according to code. It has found that each bracing system has a unique behaviour as well as different seismic parameters than other types, which are not differentiated in seismic codes such as IBC and EN. Also, it was found that the overall ductility factor, decreased with increasing the number of stories, while response modification factor (except for the inverted V-braced system) and overstrength factor increased with increasing the number of stories.