Seismic design and performance evaluation of steel braced frames with assembled self-centering buckling-restrained braces

In this study, an assembled self-centering buckling-restrained brace (ASC-BRB) is developed for seismic resilience of structures. The self-centering system of the brace mainly consists of a group of disc springs and two sets of steel strands in series to enhance the deformability and achieve the post-hardening behavior for limiting the rapid displacement development of structures under extreme earthquakes. The theoretical restoring force model is first derived according to the working principle of ASC-BRB and successfully validated by experiments. An empirical ductility demand spectral model of ASC-BRB frames is developed according to the parametric analysis on the seismic responses of the corresponding nonlinear single-degree-of-freedom (SDOF) system. The spectral model considers the influences of all independent hysteretic parameters of ASC-BRB, and the physical parameters of the brace can be determined directly from the complete hysteretic parameters. Then a displacement-based seismic design procedure for designing ASC-BRB frames is proposed. The design results indicate that the designed frames generally need at most one iterative design to meet the target performance. Although the ASC-BRBs are designed with partial self-centering behavior, the frames can still exhibit approving post-earthquake recoverability with negligible residual displacements under strong earthquakes when the values of brace hysteretic parameters are chosen reasonably. When designing ASC-BRB frames, a strength ratio beta of 0.25 and a strength ratio of steel strands eta(2) of 0.2 is recommended for improving the seismic performance and post-earthquake resilience of structures. Compared with the existing SC-BRBs with much higher initial stiffness, the proposed ASC-BRB can control the structural peak floor acceleration more effectively, which is beneficial for non-structural components.