Critical limit states in seismic buckling-restrained brace and connection designs

A welded end-slot buckling-restrained brace (WES-BRB) has been developed at the Taiwan National Center for Research on Earthquake Engineering (NCREE). A steel frame equipped with a WES-BRB can offer a cost-effective solution to meet interstory drift and earthquake-resistant design requirements for seismic steel buildings. According to the WES-BRB and connection design procedure proposed by NCREE, there are seven key elements of a buckling-restrained braced frame (BRBF) design that require design checking. In order to assist an engineer with the design of the WES-BRB members and connections, an innovative cloud service named Brace on Demand has been constructed at NCREE. In this study, using 581 BRBF design examples, the effectiveness of the proposed design procedures to meet all design checks is demonstrated. It is found that the most critical limit states for an initial design are joint region buckling, gusset plate buckling, and gusset-to-beam and gusset-to-column interface strength. Accordingly, the causes of improper designs and associated strategies for improving the initial designs are discussed in this paper. Recommendations on initial selections including the BRB joint size and gusset plate thickness are given. The paper provides the detailed road map for engineers to develop the spreadsheet for BRB and connection designs.