Post-Earthquake Fire performance-based behavior of unprotected moment resisting 2D steel frames

Abstract

Post-Earthquake Fire (PEF) can lead to the collapse of buildings that are partially damaged in a prior earthquake that occurred immediately before the fire. The majority of standards and codes for the design of structures against earthquake ignore the possibility of PEF and thus buildings designed with those codes fail prematurely when subjected to PEF. A sequential analysis based on FEMA356 is performed here on the Immediate Occupancy (IO), corresponding to a structure designed as school occupancy, and Life Safety (LS) performance levels, corresponding to a structure designed as reside ntial occupancy, of two steel moment resisting frames. These frames are first subjected to an earthquake load with the PGA of 0.35g. This is followed by a fire analysis, using both the ISO834 model and the Natural fire model. The time it takes for the structure weakened by the earthquake to collapse under fire is then calculated. As a point of reference, fire only analyses are also performed for the undamaged structures. The results show that earthquake weakened structures are more vulnerable to fire than undamaged structures. The results also show that both fire resistance and PEF resistance of the frame designed as school are more than the frame designed as residential. Whilst the investigation is for a certain class of structures (steel moment resisting frames, 5 stories), the results confirm the need for the incorporation of PEF in the process of analysis and design and provides some quantitative measures on the level of associated effects.