A Novel Approach for Addressing Interstory Drift Concentrations in Eccentrically Braced Frames

Abstract

Drift concentrations under seismic demands are accepted to be a natural phenomenon by the profession. In typical steel eccentrically braced frame (EBF) design, drift concentrations cause systems to reach their material limits at lower roof drift ratios and plastic link beam rotations to exceed permissible limits. As an attempt to demonstrate that concentrations are not natural, but rather the result of the design decisions, an algorithm to modify the drift distribution in EBFs has been developed. The developed method uses an iterative post-processing algorithm to manipulate the post-elastic modal vectors of the EBFs for distributing the interstory drift ratios uniformly and mitigating the possible drift concentrations. The algorithm proved to be effective in both design-basis earthquake (DBE) and maximum considered earthquake (MCE) demands. The initial verifications have been done through sensitivity analyses of various types of EBFs by nonlinear time-history analyses. The parameters considered are the number of stories (representing low-and mid-rise EBFs), the link length to bay width ratios (e/L), and the first story height to typical story height ratios. Results obtained demonstrated that the story shear distribution of the revised frames, which exhibited well-distributed interstory drifts, had consistent shapes markedly different from the distributions of equivalent lateral force procedures. Furthermore, base shear capacity is observed to be an important metric to be considered during the design stages. The algorithm is demonstrated by a benchmark building selected from the literature. The seismic performance of the building is enhanced through the utilization of the developed algorithm, and the outcomes are evaluated with respect to the designated metrics. The initial and ongoing observations based on the sensitivity analyses indicate the potential contributions of the developed algorithm to the efficient design of EBFs. © 2024, International Association for Earthquake Engineering. All rights reserved.