Analytical and numerical studies on reducing lateral restraints in conventional & all steel Buckling Restrained Braces

Abstract

A typical Buckling Restrained Brace (BRB) consists of a steel core and a mortar-filled tube to prevent buckling of the core. In BRBs, the mortar used in a casing considerably increases their weight. In another type of such braces, to reduce the weight, a steel casing is used to avoid buckling of the steel core. In this paper, discontinuous restraint is investigated analytically and numerically to manage buckling behavior of the core along the steel tube.In the analytical section, equations are proposed to determine a suitable distance between the restraints in rectangular and cruciform sections using inelastic buckling, tangent and double modulus theories and their combination with the Romberg-Osgood behavioral model. In the numerical section, first the cyclic behavior of 9 Conventional BRB models with continuous and discontinuous mortar casing is evaluated using the Abaqus software. Then, the appropriate distance between restraints is determined for the numerical model and compared to those from analytical equations. Results show that the tangent modulus theory is more compatible with the finite element model. Moreover, in cruciform cores, it is possible to reduce the amount of mortar up to 64% without any changes in the cyclic behavior of bracing. Finally, two all-steel BRB models are exposed to cyclic loading where steel plates prevent core bucking. Those results demonstrate that the cumulative ductility exceeds the minimum value defined by AISC.