Flexural Properties of Buckling-Restrained Brace Connections

Abstract

Buckling-restrained braces (BRBs) achieve large peak and cumulative ductility capacities by restricting yielding to an encased core, while maintaining global stability. However, stability is often governed by the connections and is sensitive to the end fixity provided by the adjacent framing and gusset, and flexural continuity between the neck and restrainer. This paper presents simple analytical methods to determine the flexural properties of these key components. Full-depth gusset stiffeners are found to be highly effective in increasing the out-of-plane rotational stiffness (KRg), equivalent to doubling the thickness. An equivalent connection is proposed to account for the adjacent framing (KRf), but this may be neglected if KRf > 10∙KRg. This is typically satisfied if a diaphragm slab and transverse beam are provided, but may exceed beam torsional bracing requirements. The restrainer end moment transfer capacity is extended to mortar-filled RHS restrainers, confirming that neck insert ratios of Lin/Bn > 2.0 are required for full continuity.

Buckling-Restrained Braces (BRB) Seismic Design - A Consulting Engineer’s Consideration

“…Research has shown beam-moment release can improve the overall performance of the connection [13]. • Out of plane yielding and buckling of gusset plates -research has shown the current AISC-341 provisions can be un-conservative and premature buckling of the gusset plate can occur [14,15]. For the NZICC connections, the following was undertaken to mitigate this design aspect: o Whitmore section local buckling check using effective length factors of ke =2.0.…”

Cyclic Loading Test of Rectangular Tube-Type Buckling-Restrained Braces with Enhancements to Prevent Local Bulging Failure

“…However, the reduced thickness makes the restrainer vulnerable to bulging because the steel core, which has undergone flexural deformation inside the restrainer, exerts an outward force on the mortar filler as the compressive force increases. Bulging is a typical failure mode of the BRB [7,8]. Lin et al (2016) and Lin et al (2018) derived a formula for the capacity of a restrainer with a rectangular tube section resisting outward forces by applying the yield line theory based on the results of finite element analysis [9,10].…”