Global buckling prevention of reduced-core-length buckling-restrained braces: theoretical and numerical investigations

An economic type of buckling-restrained braces (BRBs) to allow long spans and large capacities, the reduced-core-length BRBs (RCL-BRBs) are formed by sequentially assembling ordinary BRBs (yield portions) and ordinary braces (elastic portions) with high-strength bolts. This paper presents design recommendations for the global stability of the RCL-BRBs via theoretical and numerical investigations. In the analysis, the interaction between the yield and elastic portions of the RCL-BRBs is considered. First, the RCL-BRBs were classified into six types according to their compositions (the yield portion at one end, mid-span or both ends) and joint types (rigid or semi-rigid joint). Second, formulas for predictions of the elastic buckling loads of the RCL-BRBs were theoretically derived, and were verified by performing finite element (FE) eigenvalue buckling analyses. To investigate the nonlinear behavior of the RCL-BRBs, FE models considering both geometrical and material nonlinearities were built and calibrated with existing hysteretic tests of the RCL-BRBs. Then, a parametric study was conducted to investigate the effects of the geometrical parameters on the global stability behavior of the RCL-BRBs. Finally, based on the numerical results, the restraining ratio design requirements corresponding to the different types of RCL-BRBs were proposed to prevent their global buckling under axial compressive loads. Moreover, recommendations on the connection types between the yield and elastic portions of the RCL-BRBs are provided by analyzing a number of numerical examples.