Seismic Retrofit of Concrete Shear Walls with SMA Tension Braces

A bracing system consisting of tension-only superelastic nickel-titanium shape-memory alloy (SMA) was developed and implemented as a retrofitting methodology for seismically deficient squat reinforced concrete shear walls. The bracing system incorporates SMA links that serve as resettable fuses with unique recentering and energy-dissipation properties that result in improved hysteretic response. This paper focuses on one-third-scale walls that represent pre-1970s reinforced concrete shear walls susceptible to shear sliding and diagonal tension cracking. Four walls, two control and two retrofitted with the SMA bracing system, were tested under reversed cyclic loading. The SMA braces demonstrated excellent performance as a retrofitting device, improving the seismic response of squat reinforced concrete shear walls, including lateral strength capacity, ductility, energy dissipation, and displacement recovery. The retrofitting system was central in minimizing damage at the base of the walls.