Experimental and numerical studies on SMA-viscoelastic hybrid self-centering braces

This study presents a novel hybrid self-centering solution, namely, shape memory alloy (SMA)-viscoelastic hybrid brace (SVHB), to enhance structural seismic resilience and meanwhile, to overcome some shortcomings of existing self-centering braces. The study commences with a detailed introduction of the working principle of the SVHB, followed by a series of tests on individual SMA cables and viscoelastic dampers (VEDs). After gaining a basic understanding of the behavior of the critical components, a comprehensive experimental study on SVHB specimens considering different design parameters and loading conditions is carried out. Numerical models are subsequently developed and validated, followed by a parametric study providing a more in-depth insight into the influence of varying brace parameters. The individual SMA cables show stable flag-shaped hysteretic curves, with a fracture strain of around 15%. The individual VED displays typical parallelogram-shaped hysteretic responses, with a slight hardening effect at large shear strain. The SVHB specimen shows anticipated axial deformation mode with almost zero residual deformation upon unloading. The hysteretic response of the SVHB is the summation of that of the SMA cables and VEDs working in parallel. The average initial stiffness of the SVHB specimen is 87.4 kN mm(-1), and the equivalent viscous damping ratio is up to 14.4%. Following the experimental study, a multiple spring-based modelling strategy is proposed which can accurately capture the complex nonlinear behavior of the SVHB. The influences of various parameters, such as rate sensitivity of VED and proportion of critical components, on the behavior of SVHBs are finally revealed.