Analytical Seismic Performance Assessment of Braced Timber Frames with Shape Memory Alloy Fasteners

Abstract

The increasing adoption of mass timber construction requires a thorough understanding of its structural performance. Brace timber frames (BTFs) commonly serve as lateral load-resisting systems in mass timber buildings; however, further insight into their seismic performance, particularly regarding ductility and energy dissipation, remains essential. Shape memory alloy (SMA) dowels at BTF connections provide potential advantages due to their superelasticity, enabling large displacements with minimal permanent deformation. This analytical research investigates the seismic performance of BTFs with SMA dowel-type connections compared to traditional steel connections. The methodology involves developing a numerical framework in OpenSees to capture the nonlinear behaviour of BTFs with steel and SMA dowel-type connections. The framework involves calibrating uniaxial material models at the connection level based on experimental hysteresis results. Brace-level models incorporate asymmetrical deformation at each brace end, documented in the literature. Frame-level models facilitate pushover and time history analyses. This approach bridges the gap between experimental observations in connections and structural system applications, specifically evaluating how connection-level self-centering translates into system-level performance in moderate seismic zones in Canada. Using this numerical framework, the self-centering capacity of SMA dowel-type connections is assessed at the system-level. The seismic response of SMA-connected frames is compared to traditional steel-connected frames using BTF building prototypes. Key findings show that SMA connections exhibit superior self-centering, substantially reducing residual drift compared to steel connections, thus enhancing seismic resilience. Although SMA-connected frames experienced higher peak drifts, their minimal permanent deformations significantly reduced post-earthquake repair needs. Numerical results indicated that SMA connections increased peak interstorey drift by 8-32% but significantly reduced residual drift by approximately 90% in both prototypes. Peak floor accelerations decreased by 3-13% with SMA connections. These findings confirm that SMA dowels effectively improve post-earthquake performance without compromising structural strength. This will guide future code developments and research directions for BTF systems incorporating SMA dowel-type connections.