Seismic Performance Comparison of Moderately Ductile and Conventional Construction Steel Concentrically Braced Frames

Steel concentrically braced frames (CBFs) are widely used as a seismic force resisting system (SFRS) in Canada because of their efficiency in resisting seismic loads. Several different approaches can be taken to design CBFs according to the Canadian Steel Design Standard CSA S16:19. These approaches range from moderately ductile (Type MD) CBFs, which require special detailing considerations and limits on local and member slenderness to promote the intended ductile response, to conventional construction (Type CC), which requires higher seismic design forces but has more relaxed detailing requirements. While these construction types have been defined in CSA S16:19 for many years, few studies have compared the seismic performance of frames designed using these different sets of requirements. To address this research gap, this paper compares designs for the same archetype structure using both Type MD and Type CC CBFs. Both frame types are designed according to CSA S16:19 and subsequently modelled using the advanced earthquake simulation software OpenSees. Thereafter, the models are subjected to a multiple stripe analysis (MSA) using a set of ground motions prescribed in FEMA P-695, to assess their seismic performance. A close look at the inter-storey drift time history during a typical ground motion record reveals the sequential occurrence of the different damage states, while the statistics of the inter-storey drift ratio demonstrates that the Type CC design leads to more variable performance. Finally, storey-by-storey fragility curves are developed for both construction types to compare the seismic performance.