Effect of brace end rotation on the global buckling behavior of pin-connected buckling-restrained braces with end collars

Abstract

The effect of brace end rotation on the global stability of buckling-restrained braces (BRBs) is a common but unaddressed issue in design. To further investigate this issue, component tests of nine pin-connected BRBs with end collars were conducted, in which the effects of brace end rotation, the gap between the core and the casing, the gap between the collar and the casing and the stiffness and strength of the casing were considered. The test results show that premature global buckling still occurred even though the capacities of the specimens met the current stiffening requirement to prevent global buckling. It indicates that the commonly used global stability design criterion is not conservative. Additional end bending moments in the casing, induced by brace end rotation, would be developed if rotational gap fully developed to cause two-point contact near the casing ends. A simplified procedure to estimate the magnitudes of end bending moments is proposed. It shows that such end bending moment exceeded the yield moment of the casing when the specimens failed by global buckling, indicating a significant negative effect on global stability of BRBs. C-mode brace end rotation configuration was found to be more unfavorable than S-mode configuration for the global stability of BRBs. Several design implications and future research needs for global stability design of BRBs with pinned and bolted end connections are presented. It is suggested that the effect of end bending moment should be considered into global stability design of BRBs.