Self-centering buckling-restrained braces for advanced seismic performance

Although conventional earthquake-resisting structural systems provide adequate life safety when properly designed, 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 return to their initial position (i.e., "self-center") following an earthquake and minimize structural damage is a crucial need. This research aims to address this need by creating an innovative self-centering brace for advanced seismic performance. In the present study, the seismic behavior and performance of self-centering bucklingrestrained braces (SC-BRBs) is investigated. A SC-BRB consists of a typical BRB component, which provides energy dissipation, and pre-tensioned superelastic NiTi shape memory alloy (SMA) rods, which provide self-centering. The SMA rods are attached to the BRB portion of the brace using a set of concentric tubes and freefloating end plates that cause the SMA rods to elongate when the brace is in both tension and compression. Half-scale SC-BRBs are designed and fabricated for experimental validation. To characterize hysteretic response, the braces are subjected to a cyclic loading protocol adapted from the AISC Seismic Provisions for Structural Steel Buildings. The results of the experiments are used to validate a SC-BRB numerical model, which is used to conduct further parametric studies of SC-BRB behavior and to perform system studies of concentrically-braced frames with SC-BRBs.