Analytical and Experimental Studies on All-Steel Buckling Restrained Brace with Double Steel Tubes

This study proposes a new type of all-steel buckling restrained brace with double steel tubes composed of an inner round steel tube and an outer square steel tube, the inner core adopting a cruciform section and an H-section. These two types of cross-sectional inner cores have larger cross-sectional stiffness than round bars and better meet the requirement that inner core should be easy to yield but not easy to buckle. In this study, a theoretical design method for designing the proposed BRB in a simplified and optimal way is presented. The assembly scheme, constraint system, and overall structure are defined. The quasi-static tests of two brace specimens under a cyclic load are carried out to verify the brace's mechanical performance, axial strain distribution, and energy dissipation capacity. These results show that, relying on these two types of cross-sections, the hysteresis curves of all-steel buckling restrained braces with double-steel tubes are overall in good shape and stable. In addition, its energy dissipation performance is stable without any widespread instability phenomena. Also, the inner core has a stable plastic deformation capacity even after yielding, based on the comparative analysis of axial strain response of each components. Both specimens can meet the requirements of seismic design.