SMA tension brace for retrofitting concrete shear walls

A Shape Memory Alloy (SMA) tension brace was developed as a retrofit device to improve the seismic response of deficient reinforced concrete squat shear walls. Three, tension-only SMA braces and two, companion tension-only steel braces were built and subjected to cyclic loading. The braces consisted of SMA and reinforcing steel links, respectively, placed at the centre of the bracing system and connected to rigid hollow structural steel members. A total of four links were utilized for testing: two SMA links and two reinforcing steel links. A superelastic, nickel-titanium rod, capable of recovering large nonlinear strains was used for one SMA link; while a nickel-titanium, shape-memory rod lacking the capacity to recover strains after the removal of load was used in the other SMA link. Deformed reinforcing steel bars that experience significant residual strains during the inelastic range of loading were incorporated into the steel links. Testing illustrated that the pseudo-yield and ultimate strengths, and energy dissipation capacity of the SMA braces were comparable to the steel braces. Furthermore, the SMA braces experienced superior elongation recovery. Testing and retesting of the SMA braces illustrated their potential to act as resettable braces. Complementary nonlinear finite element analyses were conducted to assess the application of the braces to enhance the seismic response of reinforced concrete shear walls. The analyses demonstrated that the SMA braces can improve the lateral strength capacity, energy dissipation, and re-centering of reinforced concrete shear walls, while reducing strength and stiffness degradation associated with shear-related damage.