Out-of-plane stability of buckling-restrained braces including moment transfer capacity

Buckling-restrained braces (BRBs) are widely used as ductile seismic-resistant and energy-dissipating structural members in seismic regions. Although BRBs are expected to exhibit stable hysteresis under cyclic axial loading, one of the key limit states is global flexural buckling, which can produce an undesirable response. Many prior studies have indicated the possibility of global buckling of a BRB before its core yields owing to connection failure. In this paper, BRB stability concepts are presented, including their bending-moment transfer capacity at restrainer ends for various connection stiffness values with initial out-of-plane drifts, and a unified simple equation set for ensuring BRB stability is proposed. Moreover, a series of cyclic loading tests with initial out-of-plane drifts are conducted, and the results are compared with those of the proposed equations.