Experimental study and finite element simulation of innovative steel buckling restrained braces with three yielding stages

To further enhance the energy dissipation effect of graded yielding buckling restrained braces and ensure more uniform stress distribution in the bracing core, this paper proposes a novel type of three-stage yielding buckling restrained braces (Three-Stage Yielding Buckling Restrained Braces, TSY-BRB). The TSY-BRB features two weakened segments with different cross-sectional area weakening ratios to achieve three-stage yielding of the core. Static tests were conducted on TSY-BRBs with four different weakening combinations under displacement-controlled cyclic load to examine the effects of these combinations on energy dissipation capacity and mechanical properties. The results demonstrated that all TSY-BRBs exhibit a distinct three-stage yielding characteristic. Compared to the two-stage yielding anti-buckling brace, the TSY-BRB displayed a full hysteresis curve without any pinching and achieves an increased damping ratio of up to 21.8 %. The fourth TSY-BRB showed more uniform flexural behavior, indicating more uniform loading under cyclic conditions and effectively reducing stress concentration caused by area weakening. Finite element simulations were conducted and the results confirmed the hierarchical and fixed-point yielding characteristics of TSY-BRBs, with the hysteresis curves closely matching those from the tests, indicating the reliability of the test results. The in-plane deformation curve showed that the fourth TSY-BRB was stressed more uniformly and had the best overall performance.