The behaviour of buckling restrained brace system at elevated temperature

Abstract

Buckling Restrained Braces (BRB) have been widely used in the construction industry as they utilize the most desirable properties of both constituent materials, i.e., steel and concrete. They present excellent structural behaviours such as high load bearing capacity, ductility, energy-absorption capability and good structural fire behaviour. In this study, the use of BRB systems on enhancing the fire resistance of whole building in terms of preventing the progressive collapse of the structural frame against fire was investigated. The effect of size and type of filler material of existed gap at the steel core-concrete interface as well as the element's cross sectional shape on the fire resistance of BRB isolated member was explored. The accuracy of numerical solution was certified by comparing the FE results with those of analytical formulations and experimental predictions. The study in this thesis shows that the superior fire performance of BRB can be obtained by altering the filler material of the gap from metal to concrete as well as by increasing the size of the gap. Also, cylindrical cross-section BRB perform better under fire conditions compared to that of rectangular cross section. In terms of verifying the efficiency of BRBs in preventing the progressive collapse of the structural frame under fire, a new framework called "stiffness reduction" technique was proposed and the response of BRBs was compared with that of Ordinary Concentrically Brace systems (OCBs). The results indicate that BRBs provide higher global collapse temperature of the frame, owing to the greater stiffness they append to the structural frame as compared to OCBs. Moreover, BRBs are strength enough to distribute the sustained load by heated columns to the adjacent members without any buckling occurrence in the bracing member, maintaining the stability of whole frame for a longer period of heating time through both heating and cooling phases of fire.