Global Restraint in Ultra-Lightweight Buckling-Restrained Braces

Abstract

A concept for an ultra-lightweight buckling-restrained brace was conceived, and a prototype was designed that utilized an aluminum core and bundled glass fiber-reinforced polymer pultruded tubes for the buckling restraint. Prediction of global stability in compression was made using analytical methods based on single-degree-of-freedom (SDOF) and previously established Euler buckling models. Detailed finite-element simulations of the proposed prototypes utilized a constitutive model calibrated from experimentally obtained reversed cyclic coupon testing of 6061-T6511 aluminum alloy at 2–4% total strain amplitude. Analytical formulations were compared with monotonic and cyclic numerical results from a parametric study varying restrainer stiffness, end moments induced by frame drift, and core reduced section length. The study concluded that SDOF and Euler formulations may underestimate the required restrainer stiffness by a factor of two or greater. The resulting ultra-lightweight brace prototypes satisfying global buckling restraint were calculated to weigh 27 and 41% of traditional mortar-filled tube and all-steel buckling-restrained brace (BRB) configurations, respectively.