Development and experimental validation of a nickel–titanium shape memory alloy self-centering buckling-restrained brace

Buildings designed with conventional ductile earthquake-resisting structural systems are expected to provide life safety performance, but they rely on significant structural damage to dissipate the seismic energy. This structural damage and the residual drift that may result from the inelastic response can make a building difficult, if not financially unreasonable, to repair after an earthquake. As a result, development of systems that dissipate energy, minimize structural damage, and return to their initial position (“self-center”) following an earthquake is needed. This paper presents a viable solution including experimental investigation of the cyclic behavior and performance of a self-centering buckling-restrained brace (SC-BRB). A SC-BRB consists of a typical BRB component, which provides energy dissipation, and pre-tensioned superelastic nickel–titanium (NiTi) shape memory alloy (SMA) rods, which provide self-centering and additional energy dissipation. The SMA rods are attached to the BRB portion of the brace using a set of concentric tubes and free-floating end plates that cause the SMA rods to elongate when the brace is in both tension and compression. Large-scale SC-BRBs were designed, fabricated and tested using a cyclic protocol to validate the brace concept. The experimental program demonstrated that NiTi SMA SC-BRBs provide stable hysteretic response with appreciable energy dissipation, self-centering ability, and large maximum and cumulative deformation capacities.