Seismic design and analysis of truss-confined buckling-restrained braces

The truss-confined buckling-restrained brace (TC-BRB) with a varying or constant section truss confining system was proposed for applications of long span and large force capacities. Their feasibility and hysteresis behavior were examined through experimental investigations. This paper presents an original formulation of the elastic buckling resistance of the novel restraining system, considering the shear reduction effect. The findings indicate that the chord predominantly contributes to the flexural rigidity in the restraining system, while the post primarily contributes to the overall shear rigidity. Subsequently, the ultimate compressive strength of a TC-BRB is evaluated, incorporating the effects of chord residual stress, length differences between the restrainer and entire brace, and initial in-plane flexural deformation, based on available experimental data. A numerical procedure employing finite element model (FEM) analysis is introduced to simulate the mechanical characteristics of TC-BRBs. The critical loads are verified through FEM analyses and test results. The failure mode observed in the numerical models is the instability of the chords near the midspan, as expected. A simplified approach for determining the ultimate compressive strength and design recommendations for TC-BRBs are provided for engineering practice.