Evaluation of approximate methods for estimating residual drift demands in BRBFs

Nowadays, Buckling Restrained Braced Frame (BRBF) system is extensively used for the seismic design of new buildings. This system is composed of Buckling Restrained Braces (BRBs) that do not buckle under compression forces, and have high energy-dissipation capacity. However, low post-yield stiffness of the brace core in BRBs may cause large residual drifts after the occurrence of an earthquake. In this study, four approximate methods for estimating residual drift demands in BRBFs are evaluated. These methods include the FEMA P-58 method, the method proposed in this study, the method proposed by Erochko et al. and the coefficients method introduced by Ruiz-Garcia and Chora, calibrated in this study for BRBFs. To evaluate the estimated residual drifts of BRBFs according to these approximate methods, 2-, 4-, 6-, 8-, 10- and 12-story BRBFs are designed. Nonlinear dynamic analyses are performed on the BRBFs using 78 ground motion records scaled to different ground motion intensity levels. The results show that the proposed method is more accurate than the FEMA P-58 and Erochko et al. methods that are conservative for estimating the median and mean residual drifts of BRBFs, respectively. Moreover, the coefficients method, which estimates the median of maximum residual drifts, is the most accurate method among the four methods considered. However, it does not provide information about the height-wise distribution of residual drifts.