Collapse assessment of protected steel moment frame under post-earthquake fire

This paper investigates the behavior of low-, medium- and high-rise protected steel moment resisting frames under post-earthquake fire through two different methods. In the first method, the pushover analysis is utilized to simulate the response of the sample structures for various target displacements. Then the thermo-mechanical analysis is implemented to evaluate the behavior of the damaged frames under fire, assuming that the fireproofing is delaminated at the end regions of the beams. In the second method, the seismic response of the frames under two sets of the MCE-scaled near and far fault ground motion records is determined employing the time history analysis. In this method, the damage of fireproofing is characterized by the maximum inter-story drift ratio. The results of the study revealed that the method 1 give similar results to the method 2, for most cases. It is also found that for sufficiently large drift demands, the collapse of the frames under post-earthquake fire occurs in side-way mode, while for lower seismic responses, the local failure of beams dominates other failure modes. Moreover, it was found that the reduction of fire resistance time due to the effects of MCE seismic loads ranges 4% to 26% for the considered structures.