Failure Sensitivity Analysis of Tall Moment-Resisting Structures Under Natural Fires

Abstract

A series of sensitivity analyses of structural fires are performed, focusing mainly on the possibility of structural failure during the cooling phase. To investigate this, two tall ten-story steel moment-resisting buildings, with two different span lengths, 6000 and 7500 mm, but identical story height of 3500 mm, are designed for two different load combinations: gravity loads, and seismic loads. Assuming different opening ratios in a range between 0.02 and 0.2, different fire curves are created, using the EN 1991-1-2 procedure. The cases are then subjected to the fire curves to monitor their structural responses when interactions between the opening ratios, span lengths, and load combinations are considered. The results show that all of the cases meet their required FRR under all of the fire curves. The results, however, also show that, in the structures designed for gravity loads, while the span length increases, the structural vulnerability increases during the cooling phase. As well, opening ratios of more than 0.1 are seen to cause more vulnerability to the structures during the cooling phase. In the seismically designed structures, even though they are shown to be sensitive to opening ratios more than 0.1, no collapse is observed throughout the analyses.