Seismic Performance of Steel Frame Systems with Post-Tensioned Jointed Rocking Connections with Replaceable Structural Fuses Subjected to Mainshock-Aftershock Sequences

The current state of practice for seismic design of typical buildings consider only a single design level event. The recent 2010–2011 Christchurch earthquake sequences have shown the devastating effects of sequential strong ground motion events for building structures that have not been repaired post-mainshock (MS). These events highlight the need for building structures that can be rapidly repaired while also showing the critical need to consider the seismic response of these structures for cascading large seismic events, when post-MS repairs have not occurred prior to a large aftershock(s) (AS). In recent years there has been a high interest in the development of alternative seismically resilient seismic-force resisting systems (SFRSs) that offer self-centering and rapid reparability characteristics. However, compared to conventional SFRSs, these alternative SFRSs are potentially more vulnerable to large MS-AS sequences as the energy dissipation of the replaceable structural fuses are typically substantially less than those used in conventional SFRSs. Although seismically resilient SFRSs have shown to provide excellent performance under a single design level MS, their seismic performance under cascading large earthquake sequences is not well understood. This paper presents nonlinear response history analyses results of the seismic performance of two distinctly different seismically resilient SFRSs that are expected to provide frame recentering and concentrate inelastic damage to only the replaceable structural fuses. Specifically, one frame system is detailed with post-tensioned beam-to-column joints that rock about the top flanges only with a steel plate infill web plate structural fuses. The second system is detailed with post-tensioned beam-to-column joints that rock about the top and bottom flanges with tension-compression steel structural fuses. The results presented provides some insight on the system performance and seismic resiliency of these alternative SFRSs under large MS-AS sequences.