An Analytical–Numerical Hybrid Method for Evaluating Out-of-Plane Stability of Buckling Restrained Braces

Out-of-plane stability of buckling restrained braces (BRBs) has been a critical concern for structural design of them under seismic loads. Although some calculation methods are available in literature catering for the determination of stability resistance of the BRBs, they showed complexities on dealing with numbers of parameters. In this paper, the mechanism of out-of-plane buckling failure of the BRBs was firstly introduced; then, an analytically and numerically hybrid method was proposed to calculate the out-of-plane stability resistance of the BRBs with considerations given to solve some key parameters; finally, the proposed hybrid method was verified by test results of 4 BRB sub-frames subjected to the lateral loads. The results indicated that the out-of-plane bending deformation of BRB and gusset plate would occur under seismic loads. With an increasing rotation between the end of BRB and the inner core, the out-of-plane buckling failure happened owing to the existence of a plastic hinge at the bottom section of the outstanding part outside the inner core of the BRB. The out-of-plane bending stiffness of BRB and gusset plate, initial imperfection and bending moment capacity of the outstanding part are the key parameters affecting the out-of-plane stability of the BRBs. The proposed hybrid method is reasonable and effective to calculate the out-of-plane buckling capacity of the BRBs subject to different combinations of axial force and end bending moments.