Subassemblage tests and design of steel channels assembled buckling-restrained braces

This study investigates the load-carrying behavior of a proposed all-steel buckling-restrained brace (BRB) under seismic loading. The proposed steel channels assembled BRB (SCA-BRB) consists of a steel core plate encased by four steel channels assembled by high-strength bolts. Self-weight of an SCA-BRB is relatively small since the use of concrete is eliminated, leading to easier transportation and erection of the BRB. Firstly, by simplifying the restraining system of an SCA-BRB into a 2-chord battened column, the reduction factor of the elastic buckling load of the restraining system considering the discrete connection of bolts was derived. On this basis, the formulas in predicting ultimate resistance of an SCA-BRB were deduced along with the formulas of the lower limit of restraining ratio, and the upper limit of bolt spacing. Then, subassemblage test results of four specimens were reported. All the test specimens maintained stable load-carrying capacity during the loading process, and satisfactory energy-dissipating ability was achieved. Finite element (FE) models were established, and they well predicted the hysteretic responses of the test specimens. A total of 25 additional FE models was analyzed to perform a parametric study, verifying the effect of the member length, number of bolts, steel grade, gap size and geometrical imperfection on the hysteretic response and ultimate resistance of BRB. Finally, a design procedure of the SCA-BRB was proposed based on theoretical formulas, which have been validated by tests and FE results.