A study on effectiveness of buckling-restrained braces in mitigating earthquake response of framed buildings

Steel bracing members are widely used in the structures to reduce lateral displacement and dissipate energy during earthquake motions. However, under cyclic loads such as earthquake, the bracing members are subjected to cyclic tension and compression axial loads which results in buckling of bracing members, increase in member lateral displacements and reduction in the load resistance capacities. In recent years, to overcome this negative behavior of bracing members, significant research efforts have been intended for developing buckling restrained bracing with stable hysteretic behavior, significant ductility, and large energy dissipation. In this study, a numerical investigation is presented on the effectiveness of BRBs to protect and mitigate response of structures subjected to lateral loading. For this, nonlinear static analysis was performed in order to examine the seismic behavior of different ordinary and buckling restrained braced frame buildings. As a case study, 2, 4, 6, and 8 storey ordinary moment resisting steel frame buildings were designed with lateral stiffness insufficient to comply with drift limitations given in FEMA 356. Frames of each building had equal four bays of 5 m. Then, BRBs with different configurations, namely chevron, diagonal, split-X, and V-bracing systems were inserted into the exterior bays of each building. The performances of the frames with and without BRBs were investigated through nonlinear analysis. As a result of the analysis, inter-storey drift index, global damage index, capacity curves, plastic hinge formations, and deflected shape were obtained for the bare frames and buckling restrained braced frames and discussed comparatively.Keywords: Buckling-restrained brace; Ordinary frame; Performance characteristics; Structural response.