Experimental Study on Mechanical Properties of Double-Stage Yield Buckling Restrained Braces

With the growing demand for seismic resilience in urban building structures, the development of high-performance energy-dissipation components has become critical for enhancing structural safety and mitigating earthquake-induced damage. Traditional buckling restrained braces (BRBs) are typically designed to remain elastic under frequent earthquakes, limiting their ability to dissipate early seismic energy input. To address this limitation, a novel friction-damped double-stage yield buckling restrained brace (FD-DYBRB) is proposed by integrating friction dampers (FDs) with a conventional BRB. The mechanical performance of both the traditional BRB and the proposed FD-DYBRB was investigated through cyclic loading tests. Additionally, to evaluate the performance differences among various configurations, a cross-shaped double-stage yield BRB was also tested for comparison. The experimental results demonstrate that the proposed FD-DYBRB design is highly effective, exhibiting plump hysteretic curves and distinct double-stage yielding characteristics. Specifically, the FD-DYBRB possesses an initial stiffness ranging from 249.38 kN/mm to 250.31 kN/mm, which is comparable to traditional BRBs. Under small displacements, its equivalent damping ratio increases by approximately 7% for every 50 kN increase in friction force, achieving continuous early-stage energy dissipation. Furthermore, the proposed brace realizes full-process energy dissipation by maintaining stable average tensile and compressive capacities of 87.08 kN and 84.50 kN, respectively, even after the core plate fractures. Compared to the traditional BRB, the maximum dissipated energy of the FD-DYBRB increases by 23.55% to 54.75%, and its maximum equivalent damping ratio exceeds that of the cross-shaped DYBRB by 5%. These findings offer a reliable technical solution for improving the seismic performance of high-rise and long-span buildings, ultimately helping to mitigate structural damage and protect life and property during seismic events.