Self-centring behaviour of steel and steel-concrete composite connections equipped with NiTi SMA bolts

This paper reveals the great potential of using NiTi shape memory alloy (SMA) bolts for self-centring connections against seismic action, with the main focus on the influence of composite slab systems on the connection performance. An experimental study on four full-scale specimens, including two SMA-based bare steel connections and two composite connections, is conducted. The results show that the steel specimens, classified as semi-rigid and partial-strength connections, exhibited satisfactory self-centring ability and ductility. For the composite specimens, due to the yielding of the reinforcement and metal deck, accompanied by cracking of the concrete slab, the self-centring ability is compromised to a certain extent. All the connections showed moderate energy dissipation capacity, with a stable equivalent viscous damping (EVD) of approximately 10% at large deformations. A comprehensive numerical study, employing an efficient yet simple way to capture the actual cyclic performance of the SMA bolts, is subsequently conducted, and the validated modelling approach is used to conduct a further parametric study, discussing the influences of bolt preload, reinforcement, metal deck orientation, and slab insulation. A preliminary design recommendation is also proposed based on the test data and the numerical study results.