Rotation Capacity of I-Shaped Beam Failed by Local Buckling in Buckling-Restrained Braced Frames with Rigid Beam-Column Connections

Abstract

A buckling-restrained braced frame (BRBF) reduces the response of buildings during a strong earthquake, during which the surrounding members such as beams and columns must resist the axial force imposed by the buckling-restrained braces (BRBs). However, the steel beams and columns are subjected to reversed axial force from the horizontal and vertical component of BRB axial force. The steel beams might then buckle under the compressive force or even yield under the subsequent tensile axial force because the beams are not designed primarily to sustain the axial force. Therefore, the rotation capacity becomes inconsistent with the typical loading protocols. Faced with this concern, this study examines a BRBF design with reasonable balance between the steel frame and the BRBs. Pushover analyses and nonlinear response history analyses (NRHAs) are undertaken to quantify the magnitude of the beam axial force. Furthermore, a detailed finite-element analysis (FEA) model is constructed based on results obtained from a previous experiment. The strain distribution and axial force transfer mechanism are identified using an experimentally validated FEA model. Results confirm that BRB axial force is transmitted primarily to the single side of the flange. Furthermore, the parametric study in terms of the beam section, BRB axial force, and loading protocols establishes a database of the structural performance. The results of this research are used to formulate a novel index and equations describing the ultimate strength ratio, rotation capacity, and energy dissipation capacity.