Behaviour of buckling-restrained brace equipped with steel and polyamide casing

Steel bracings are one of the most widely used systems for resisting transverse loads in the design and retrofit of concrete and steel structures. This paper reports on an experimental and numerical study of the effects of core steel and the distance of the core from the casing on the behaviour of buckling-restrained braces. Laboratory models of six braces with a core made from conventional ST37 steel or ST37-n steel (softened at a temperature of 1000° using the O'Neill method) with a core–casing distance of 0, 2 or 3 mm were designed. The experimental results showed that, compared with the brace made from ST37 steel, the use of ST37-n steel resulted in a reduction of 32% in the tensile and compressive strengths of the brace. An increase in the core–casing distance in the ST37 and ST37-n braces resulted in reductions in the brace bearing capacity and energy dissipation by 26% and 52%, respectively. An increase in the core–casing distance to more than 2 mm resulted in loss of symmetry and stability of the hysteresis behaviour of the brace; in addition, distortion due to brace local buckling under pressure also intensified.