Hysteretic behavior of a tandem self-centering double-stage yielding buckling-restrained brace

This paper proposes a tandem self-centering double-stage yielding buckling-restrained brace (TSCDY-BRB). A staged-stiffness restoring-force model and a three-dimensional finite element model are developed and validated against quasi-static tests, and reproduce the hysteretic response within about 15% error. The brace exhibits stable flag-shaped hysteresis, transitioning from a single-flag loop at small drifts to a flag with a second yielding plateau after the Group-2 cores engage. Parametric studies indicate that prestress sets the strength baseline and controls recentering; strand diameter influences post-activation stiffness; the Group-1 core area dictates initial strength, stiffness and low-amplitude energy dissipation; the Group-2 core area governs Stage II strength, stiffness and high-amplitude dissipation; and a larger preset gap delays Stage II activation, improving recentering but reducing damping. Within the studied range, single-cycle energy dissipation reaches 6.5–10.5 kJ, with an equivalent viscous damping ratio of 0.12–0.17, and the residual-to-peak displacement ratio remains below 3% with suitable prestress and gap. For design, an initial prestress about 1.5 times the combined yield force of the two core groups is recommended, and the preset engagement gap and the yield displacement of the Group-2 cores should be coordinated with the target peak displacement to ensure effective recentering and staged energy dissipation. System-level analysis of a six-story steel frame shows that, compared with a double-stage yielding BRB frame of identical initial properties, the TSCDY-BRB frame achieves much smaller residual drifts while maintaining comparable peak drifts under 0.2 g and 0.4 g excitations, confirming its effectiveness over different seismic levels.