SEISMIC BEHAVIOR OF BUCKLING RESTRAINED BRACES WITH STEEL TUBE WITHOUT MORTAR FILLER

One of the methods for stability of structures under seismic loads is the use of steel braces. One of the bracing systems with appropriate performance is Buckling Restrained Braces (BRBs.). This kind of braces does not have weakness such as the conventional concentrated braces under cyclic loading and provides significant capacity of energy dissipation with members restrained from buckling and has symmetrical and stable hysteresis curves. This system serves as replaceable structural fuses, minimizing the amount of damage to the other members. These studies have been conducted to the restrained buckling braces systems. Most of the cases have been surrounded by the concrete or mortar and the metal sheath. Since the construction of the
bracing surrounded with filler material has difficulties, it was necessary to study another type of braces on wich few studies have been conducted. In this research, 11 models of BRB have been studied. selected for the investigation of Buckling Restrained bracing members, including flat plates, cross, double, and circular studs which are without filler, have been surrounded by metal sheath in ABAQUS software. Modeling parameters and lack of enforcement of mortar filler, shape of the core,thickness of sheath are specified by examining the ratio of buckling load of sheath (Pe) to yield load of core (Py) under cyclic loading. The results have shown that the capacity of energy dissipation of BRB is about 12 times more than the capacity of conventional concentrated braces. The increase of tolerance has been brought about by increasing the ability of the energy dissipation. In addition energy dissipation capability and the maximum capacity of section in the state without filler materials decrease, and the core of circular section is more resistant than the cross and studs sections. Energy dissipation capacity with circular cross-section is
compared with the channel and cross section. By increasing the tolerance limit, load model has decreased; however, energy dissipation capability has increased.