Comparative study on the behaviour of Buckling Restrained Braced frames at fire

• We study Buckling Restrained Brace (BRB) response in resisting frame collapse at fire.
• BRB suffer fire heating and cooling phases but the ordinary type stands just the former.
• BRB enhance frame fire resistance due to its similar tension and compression response.

In this paper, the use of Buckling Restrained Brace systems (BRBs) in preventing the progressive collapse of the structural frame against fire is investigated using the stiffness reduction technique. Four-storey steel structures fitted with different bracing configurations were modelled using the Vulcan programme. For comparative purpose, the efficiency of BRBs in preventing the progressive collapse of the structure is compared with the Ordinary Concentrically Brace systems (OCBs) in the presence of edge and central bay fire exposures. In order to consider the effect of bracing member stiffness on the collapse prevention of the frame and to provide a comprehensive scheme of progressive collapse mechanism under fire condition, several cross sections of BRBs under different fire scenarios are considered. The results indicate that BRBs provide a higher global collapse temperature for the frame, owing to a greater stiffness and more symmetrical performance offered as compared to OCBs, and thus providing better progressive collapse resistance. Moreover, it is observed that BRBs are stiff enough to redistribute the sustained load by heated columns to adjacent members without any buckling occurrence in the bracing member, maintaining the stability of the whole frame through both heating and cooling phases of fire.