Post-tensioned mass-timber moment-resisting frames for canadian applications: seismic design and performance evaluation

Canada’s pursuit for low-carbon construction has encouraged a wider adoption of mass-timber buildings. In regions of high seismic risk, low-damage and resilient mass-timber seismic force-resisting systems (SFRSs) are crucial. Originally developed and tested at the University of Canterbury, post-tensioned mass-timber moment-resisting frames (PT-MT-MRFs) have emerged as a promising SFRS for low- and mid-rise mass-timber buildings. Compared to conventional mass-timber moment-resisting frames with ductile connections, this innovative system exhibits a self-centering behaviour and enhanced ductility achieved through a controlled rocking mechanism at beam-column joints supplemented by energy dissipation from metal dampers. While PT-MT-MRFs have already been adopted in practice in countries such as New Zealand and Switzerland, their seismic design and performance have not been fully investigated in Canada, particularly in high seismic risk regions like Southwestern British Columbia. To address this gap, two-, four-, six-, and eight-storey PT-MT-MRFs archetype buildings in Vancouver, Canada, were designed using a direct displacement-based design (DDBD) methodology and evaluated using the performance-based unified (PBU) procedure. A multi-spring-based numerical modelling approach, developed in OpenSeesPy and validated against component and shaking table test results, was used to model the archetype buildings. A probabilistic seismic hazard analysis with seismic disaggregation was conducted to quantify the relative contributions of various earthquake types to the regional seismic hazard. Subsequently, for each archetype, eighty hazard-consistent and structure-specific ground motion records were selected based on Vancouver’s Conditional Spectra and scaled to the design spectra in accordance with the 2020 National Building Code of Canada. Nonlinear response history analyses were performed to evaluate structural performance against NBC drift criteria under design-level intensity, while incremental dynamic analysis results were used to assess the system’s performance margin ratios and derive fragilities. Overall, the findings demonstrate the strong potential of PT-MT-MRFs as a sustainable and resilient SFRS for low- and mid-rise construction in high-seismic regions of Canada.