A Damage Index for the Seismic Evaluation of Buckling-Restrained Braces

This paper focuses on evaluating whether a buckling-restrained brace (BRB) element should be replaced after an earthquake event. For this purpose, a damage index is proposed based on the experimental data obtained from a series of tests conducted on different BRB specimens. In total 19 full-scale BRB specimens were manufactured with local industry and workforce, and tested. 14 BRB specimens were tested using a low-cycle loading protocol, and five BRB specimens were tested using a high-cycle fatigue loading protocol. For the low-cycle protocol, the axial strain in the BRB core was continuously increased until failure, while for the fatigue protocol, the axial strain in the core was increased from zero to 1.5%, and continued at 1.5% strain until core failure occurred. The proposed damage index has been calibrated based on the experimental results, and is capable of considering the effect of the maximum core strain attained as well as the cumulative deformation effect. A qualification scale has been assigned to the proposed damage index as a tool for evaluating whether the BRB element should be replaced or left on site. Furthermore, a series of nonlinear dynamic analyses were carried out on a sample building in order to validate the proposed damage index when subjected to ground motions. Finally, the results suggest that the proposed damaged index can be useful in structural design practice.