Numerical evaluation of the hysteretic behavior of concentrically braced frames and buckling restrained brace frame systems

This paper presents a numerical investigation of buckling restrained brace (BRB) frames (BRBF) and a comparison with concentrically braced frames (CBF). A simplified core-spring finite element model was used to model BRB elements. Four types of CBF (X, V, inverted V, and two-story X) and four types of BRBF (diagonal, V, inverted V, and two-story X) were modeled in ABAQUS. A static nonlinear pushover analysis considering two cyclic loading protocols showed that the buckling restraint allows the BRB elements to undergo significant plasticity without forming plastic hinges, thereby dissipating a proportionally larger amount of energy and delaying yielding in the frame elements. Results indicated dramatic improvements in energy dissipation and ductility in BRBF models as compared to equivalent CBF models. Seismic response modification factors for BRBF models also showed greater values over CBF models. Time-history analysis evaluated the performance of CBF and BRBF under historical earthquake loadings and supported the same conclusions. The best performance was observed for V, inverted V, and two-story X BRBF configurations; the diagonal BRBF configuration performed better than equivalent CBF models, but did not perform nearly as well as the other BRBF models.