FEA Strategy for Realistic Simulation of Buckling-Restrained Braces

Buckling-restrained braces (BRBs) are seismic devices that provide structures such as buildings and bridges with lateral support, dissipating more energy than traditional bracing. Large-scale laboratory testing to assess every buckling-restrained braced frame (BRBF) is desirable but cost prohibitive. Computer simulation that incorporates realistic BRB mechanical behavior is an attractive option to supplement such testing. Predicting the cyclic response and ensuring stability of BRBFs during severe earthquake events is of particular interest. A finite-element analysis (FEA) strategy that can model the testing of BRBs was developed using Abaqus software. The development of nonlinear material and contact models are important aspects that affect accuracy and convergence in each model. The Chaboche method, using six back-stress curves, is used to characterize the combined kinematic and isotropic hardening exhibited in the steel cores of BRBs. A simplified approach was developed to capture the contact interaction between the restrainer and the core of each BRB design modelled. Each model captures important frictional dissipation as well as lateral motion and bending associated with higher-order constrained buckling of the core in both the strong and weak axis. At the same time, the methodology sought to minimize computational expense for this highly nonlinear system. The strategy was validated by comparing cyclic axial force versus displacement predictions to experimental data for three different BRB designs. This modeling strategy could be helpful for simulating the performance of other generic BRB designs and subassemblages.