Global buckling prevention of end collared buckling-restrained braces: Theoretical, numerical analyses and design recommendations

In recent years, buckling-restrained braces (BRBs) have been widely utilized in engineering structures. Generally, BRBs are diagonally installed in frame structures to serve as lateral-resistance and energy-dissipation members. To prevent the local buckling of the unrestrained portion of a pin-ended BRB, an end collared BRB (EC-BRB) was proposed by prior researchers by installing end collars at both ends of an ordinary BRB. By using this approach, the enhancement construction of the unrestrained portion could be remarkably simplified, and the end collars can provide lateral restraints to the restraining member, thus improving the global stability of the BRB member. In this paper, a design method for global buckling prevention of pin-ended EC-BRBs based on the restraining ratio requirements is provided via theoretical and numerical analyses. The equation of elastic buckling loads of EC-BRBs is firstly derived and validated by the eigenvalue buckling analyses via ANSYS, and the restraining ratios of EC-BRBs could be further calculated. Then, the restraining ratio requirements of EC-BRBs are theoretically proposed based on the magnification factor of the mid-span lateral deformation, and accordingly a recommended design procedure is provided. The design procedure is further validated by numerous finite element (FE) models subjected to hysteretic and monotonic loadings, indicating that this procedure can conservatively ensure the global stability of EC-BRBs and it is suitable for practical engineering applications.