Investigating Approximate Methods to Predict Residual Interstory Drift Ratio Demands in Steel Eccentrically Braced Frames

Residual drifts after earthquakes are important for decision-making about repairing or rebuilding a structure. There are some approximate methods that predict the residual drift demands of structures after earthquakes. Most of the approximate methods have been proposed for structures with moment resisting systems. Recent studies have shown that eccentrically braced frames (EBFs) can have considerable residual drifts after earthquakes. In the present study, the capability of approximate methods (including the Erochko et al., FEMA P-58, and coefficients methods) for predicting residual interstory drift ratio (RIDR) demands in low- to mid-rise steel EBFs is evaluated, given different ground motion intensities. Two types of connections (i.e., fixed and pinned) are considered for the EBFs. It is shown that these approximate methods cannot accurately predict the RIDRs in the EBFs, and the obtained predictions are significantly over-predicted in some cases. Furthermore, it is shown that the RIDR profile can considerably differ by changing the type of connections. By applying the particle swarm optimization algorithm, a new method is proposed for more precisely predicting the median RIDR profile in the EBFs. Additionally, the coefficients method is adjusted to more precisely predict the median of maximum RIDRs in the EBFs.