Higher‐mode buckling and friction in long and large‐scale buckling‐restrained braces

Abstract

Summary Buckling‐restrained braces (BRBs) are widely used as energy‐dissipation members in seismic areas, and BRBs with 10–20 m workpoint lengths have been applied in practice, particularly in tall buildings and spatial structures. This paper investigates the adverse effects of the core yield length on the compressive overstrength factor, local compressive and tensile strains, and fatigue demands. Sets of 2D shell and 3D solid models were analyzed using Abaqus, considering core yield lengths of up to 14 m and LY100, LY225, SN400B, SN490B, SA440B, and SA700 steel grades. Higher‐mode buckling and friction were shown to significantly amplify the compressive strain at the core ends and tensile strain at midspan, in part due to cyclic strain ratcheting, introducing the potential for core binding and premature necking. From these results, simple equations were proposed to calculate the compressive overstrength factor and to select the larger strong axis debonding gap and smaller design strain required for long BRBs.

Experimental Investigation of Friction at Buckling-Restrained Brace Debonding Interfaces

“…No codified test protocol currently exists to systematically obtain the friction coefficient for BRB debonding interfaces, and the contact and slip demands that may plausibly be encountered in practice are not well understood. Therefore, a parametric study (Sitler and Takeuchi 2021) of 576 Abaqus/Explicit 2017 models (Smith 2017) was postprocessed to characterize the maximum and minimum bearing pressures, slip velocities, and slip distances and narrow the test specification.…”

“…Secondly, half-length two-dimensional (2D) models were adopted to improve runtime. These conservatively capture the demands at the plate edges, as three-dimensional (3D) anticlastic plate deformation reduces contact over the middle of the rectangular core plates (Sitler and Takeuchi 2021). BRB failure modes, such as global buckling and bulging, were not modeled to avoid arbitrarily limiting the analysis by a design-specific capacity.…”

“…The protocol consisted of two cycles each at an average axial strain of ε ¼ δ=L p ¼ 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%, which was applied sinusoidally at a 2 s period for the velocity-dependent models. The constitutive material models and further details are provided in Sitler and Takeuchi (2021).…”