Key parameters influencing performance and failure modes for BRBs using nonlinear FEA

Conventional concentric braces buckle under compressive loading. To overcome this limitation, the Buckling-Restrained Braces (BRBs) were introduced in the mid 70s. They typically consist of a low-yield steel core and a restraining mechanism. In order to achieve enhanced understanding of the design parameters that have the most impact on the BRB inelastic behavior and failure mechanisms, comprehensive experimental efforts are typically needed. When such experimental programs are unfeasible or impractical, other investigative means are valuable. The presented paper explores the most influential BRB design parameters as well as the common failure modes observed. This is achieved through detailed nonlinear Finite Element Analysis (FEA). The FEA is carried out using the commercial software ABAQUS taking into consideration both material and geometric nonlinearities. The FE model is meticulously verified against experimental tests reported in the literature and good correlation is observed. The verified FE model is further utilized to perform a deterministic sensitivity analysis and simulate different failure scenarios for BRBs under cyclic loading. It is found that among the different failure modes, necking of the steel core is potentially the most serious. It could trigger significant internal damage to the BRB upon subsequent compressive load reversal leading to failure of the entire brace through significant internal damage or global buckling.