Seismic Design and Performance of Buckling Restrained Braced Frames with Eccentric Brace Configurations Part 1: Design Procedure and Case Studies

Abstract

Buckling-restrained braced frames (BRBFs) are a widely used lateral system comprised of beams, columns, and diagonal buckling restrained braces (BRBs). The BRBs within these frames are typically oriented concentrically. Current U.S. design provisions limit the eccentricities in BRBFs to less than the beam depth, which results in less architectural flexibility as compared to eccentrically braced frames (EBFs). The purpose of the present study is to investigate the design and performance of BRBFs with larger beam eccentricities. BRBFs were designed with beam eccentricities ranging from 0 (control case) to 2 times the beam depth in the chevron (inverted-V) and single-diagonal configurations. In each case, the beams were designed to remain elastic under the maximum forces that could be delivered by the braces, including the effects of the brace eccentricity on the beam. Nonlinear response history analysis and pushover analysis were used to quantify the performance of the various frames under design earthquake shaking and to investigate the relationship between BRBF beam eccentricity and seismic performance for the cases considered. The results of this study are presented in a two-part paper. This paper, constituting Part 1, describes the design procedures for BRBFs with eccentricity in chevron and single-diagonal configurations. Analysis methods for determining force demands in braces, beams, and columns are presented. The analysis methods are illustrated through the design of nine case study buildings. The designs show the impact that eccentricities have on member sizing and overall frame weight. For chevron BRBFs, eccentricities of 1 to 2 times the beam depth resulted in overall frame weight increase of 1.07 to 1.32 times, due to heavier beams. For single-diagonal BRBFs, eccentricities of 2 times the beam depth resulted in a slight reduction of overall weight, due to moment frame action associated with the eccentric beam stub. The accompanying paper, Part 2 (Li et al., 2026), presents the nonlinear analysis studies, including response history analyses and pushover analysis, for evaluating the seismic performance of these nine case study designs.