Seismic Performance of Concentrically Braced Steel Frames Equipped with Novel Self-Centering Dual-Stage Yielding Buckling-Restrained Braces

Conventional buckling-restrained braces provide stable and efficient hysteretic energy dissipation but lack a recentering mechanism and adequate deformation capacity, which may result in significant residual deformations after strong earthquakes. Conventional self-centering braces reduce residual deformation but often provide limited energy dissipation under large seismic demands. To address these complementary limitations, a novel self-centering dual-stage yielding buckling-restrained braces is proposed. The device uses a two-stage core. A shape memory alloy first-stage core provides recentering. A low-yield-point steel second-stage core provides supplemental energy dissipation. An activation-displacement mechanism controls staged engagement of the two cores. Experimental tests validate the feasibility of the proposed configuration and confirm its stable hysteretic behavior and reliable recentering performance. A six-story concentrically braced steel frame is subsequently modeled in OpenSees, and nonlinear time-history analyses are performed to evaluate the seismic response of the system. Under an equal initial-stiffness design criterion, the seismic performance of frames equipped with the proposed brace is systematically compared with those incorporating a conventional self-centering brace and a conventional buckling-restrained brace. The numerical results indicate that the proposed system achieves enhanced control of interstory drift, mitigates weak-story behavior, and effectively reduces residual deformation under different seismic hazard levels while promoting a more uniform distribution of deformation along the structural height. Furthermore, a comprehensive parametric study is carried out to clarify the influence of key design parameters on displacement response and recentering performance, providing practical guidance for the seismic design and engineering application of the proposed brace.