Behavior of concentrically braced steel frames under fire loading

The necessity to better understand how a steel structure behaves under fire loading has gained significance, since a large number of recent events have proved the vulnerability of steel structures under such hazard. Older concentrically braced frames have been widely used in buildings, which had been formerly designed without observing seismic provisions and details. Although the vulnerability of this type of structural systems, here referred to as non-seismic braced frames, under earthquake loading has already been studied, its behavior under fire loading has not been investigated yet. Therefore, this study aims to investigate the behavior of global and local responses of the mentioned structural system under various uniform fire scenarios. The heating and cooling phases of fire were taken into account for different building stories using the finite element method. The results of the conducted analyses demonstrated that the braces buckled at high temperatures due to large compressive axial forces and expansion of lateral constraints. This phenomenon led to early loss of the lateral resistance of stories, which, in turn, resulted in the failure of columns. Consequently, the underlying oor collapsed under fire. The analysis results contributed to a better understanding of the behavior of steel braced frames under fire conditions.