Cyclic Behavior and Damage Assessment of Superelastic SMA Dowel Connections for Braced Timber Frame Applications

Abstract

Braced timber frames (BTFs) are an efficient lateral force resisting system that can effectively resist wind and earthquake loads. It is well-known that the performance of BTFs is strongly dependent on connection behavior, but clear design guidelines are not available for detailing ductile BTFs. Furthermore, conventional connections with steel fasteners can exhibit significant stiffness and strength degradation under earthquake loads and result in large residual deformations. There is a need for more resilient energy-dissipating connections for BTFs and other mass timber systems. This study investigates the behavior of dowel-type and bolted wood-steel-wood connections with superelastic nickel-titanium (NiTi) shape memory alloy (SMA) fasteners. Under bending, the SMA fasteners are able to effectively recover their original shape with negligible residual deformation, even after undergoing large deflections. The SMA connections tested in this research showed significant potential for self-centering. Post-test autopsies of the connection test specimens showed ductile deformation mechanisms and similar levels of wood crushing between the steel and SMA fasteners under cyclic loading. However, the connection displacement ductility ratios of 4.6 and 6.2 observed with SMA fasteners is not sufficient to meet the requirement for moderately ductile frames. Additional research is required to better understand and characterize the behavior of SMA connections at the component and connection levels.