A Post-Earthquake Fire Factor to Improve the Fire Resistance of Damaged Ordinary Reinforced Concrete Structures

Abstract

Post-earthquake fire (PEF) is considered as one of the most problematic potentially possible disasters in urban areas, as it may result in a conflagration. Most standards and criteria, however, ignore the possibility of fire after earthquake and therefore, majority of conventional buildings are not designed to resist thermal loading after an earthquake. Thus, there is high likelihood of rapid collapse for those buildings damaged partially after an earthquake, which are subjected immediately to a following fire. An investigation based on sequential analysis inspired by FEMA356 is performed in this paper on two RC frames; three and five stories at the Life-Safety performance level and designed to the ACI 318-08 code after they are subjected to a spectral PGA of 0.35g. This is followed by a five-hour fire analysis of the weakened structures, from which the time it takes for the damaged structures to collapse is calculated. As a point of reference, the fire resistance is also determined for undamaged structures and before the occurrence of earthquake. The results show that the structures previously damaged by the earthquake and exposed to PEF are more vulnerable than those that are not damaged. A CPEF greater than 1 is then introduced as a function of fire extinguishing or evacuating time that can be multiplied by the base shear at the time of design in order to increase members sizes and thus improve the PEF resistance. Whilst the investigation is for a certain class of structures (ordinary buildings, intermediate reinforced concrete structure, three and five stories), the results confirm the need for the incorporation of post earthquake fire in the process of analysis and design, and provides some quantitative measures on the level of associated effects.