Behavior of NiTi Shape Memory Alloy- and Steel-Reinforced Shear Walls Repaired with Engineered Cementitious Composite

This paper presents the results of an experimental study investigating the response of two shear walls repaired with engineered cementitious composite (ECC). One of the walls was reinforced in the boundary regions within the plastic hinge with superelastic, nickel-titanium (NiTi) shape memory alloy (SMA) bars, while the companion wall was reinforced with deformed mild steel bars only. The repair method involved the removal of the heavily damaged concrete in the plastic hinge zone, replacement of ruptured and buckled steel reinforcement, placement of starter bars at the base of the walls, and casting of ECC to replace the removed concrete. The SMA bars were reused as they sustained no damage from the initial testing. Summarized in this paper are an assessment of the performance of the repaired walls and a comparison with the responses of the walls previously tested in their original condition. The experimental program highlights the enhanced performance of the composite system that integrates the self-centering capabilities of SMA bars and the distinctive tension strain hardening and ductility of ECC. The lateral strength was markedly increased, while the energy dissipation and recovery capacities, in general, were improved for the repaired walls compared to the original walls. The repaired steel-reinforced wall developed a peak lateral strength of 23% larger compared to the original wall, while the repaired SMA-reinforced wall had a 16% increase in peak lateral strength compared to the original specimen. The strength enhancement of the repaired walls led to higher dissipated energy throughout testing. For both sets of walls, the SMA-reinforced walls exhibited larger rotations compared to the steel-reinforced walls primarily on account of the lower stiffness of the SMA bars.