Hybrid self-centering braces with NiTi-SMA U-shaped and frequency-dependent viscoelastic dampers for structural and nonstructural damage control

This study proposes a novel hybrid self-centering brace (HSB) with structural and nonstructural damage-control capabilities for the seismic resilience of building structures. NiTi-based shape memory alloy (SMA) U-shaped dampers and frequency-dependent viscoelastic dampers are included in HSBs to provide self-centering capacity for avoiding structural damage and velocity-proportional damping for nonstructural damage control, respectively. This study includes two major parts, i.e. component-level mechanical behaviour and system-level dynamic response evaluation of HSBs. The working principle and desired nonlinear behaviour of the HSB were first presented. Then, the preliminary design procedures were developed. After validating the efficiency of the modelling of SMA U-shaped and viscoelastic dampers using prior test results, comprehensive 3D finite element model simulations were performed to study the hysteretic responses of HSBs under cyclic loadings, where the influences of loading frequency, loading amplitude and viscoelastic damper's contribution were considered. Analysis results demonstrated that the designed HSB can attain the desired deformation mechanism and nonlinear hysteretic behaviour during dynamic cyclic loadings. Higher loading frequency and amplitude and more contributions of the viscoelastic damper can introduce higher loading and energy-dissipation capacity. Subsequent dynamic analyses of the single-degree-of-freedom systems were conducted to assess the dynamic performance and advantages of HSBs. Results showed that compared with traditional self-centering systems without velocity-proportional damping, the systems with HSBs can achieve zero residual deformations, lower base shear demands and smaller absolute acceleration responses, confirming the promising potential of HSBs in developing seismic resilient building structures by reducing structural and nonstructural damage.