Abstract

The potential of fire event after a strong earthquake is quite high and the damage caused by this fire could be significantly higher as compared to normal fire not accompanied by an earthquake. Thus it is important to know the behavior of structures under such circumstances. Modern buildings are designed to have adequate resistance against an expected level earthquake, and sufficient fire safety, considering these events to occur separately. However, fire following a seismic excitation is not uncommon. After an earthquake the structure may sustain a considerable damage and the fire resistance of the system will be significantly impaired. In this case, the fire performance of the structure will be significantly reduced, and such condition may pose a serious threat to structural integrity, which is detrimental to the life safety of the occupants and rescue workers. Thus, it is necessary to consider such scenarios in the design of a building constructed in a seismic zone. In this study the performance of two types of structures has been studied. Load bearing wood stud walls and moment resistant steel frames under such condition has been modeled and analyzed. The performance analysis of the wood stud wall in fire has been verified with the results from the NRC fire tests. For the steel frames, the results are validated with different finite element systems such as SAFIR and ANSYS. The analysis includes heat transfer analysis and thermal stress analysis by using numerical model for wood wall and finite element solver for steel frame. Existing numerical model for stability analysis of wood frame walls cannot be applied to cases with fire and earthquake induced fire. Modifications are proposed to the existing methods in order to account for the time dependent changes in strength, stiffness and geometry due to earthquake and fire in order to determine the fire resistance of the structures. Two analytical approaches have been proposed for modeling the damage in the steel structure after earthquake. Fire resistance rates are investigated for both normal and post earthquake fire scenarios. It is observed from the study that the fire followed by an earthquake reduces the fire resistance of a structure in both wood-frame and steel-frame structures. The study presented here forms a preliminary understanding of the PEF phenomenon and its effect on structures. Further studies are needed to enhance the understanding, quantify the parametric changes and formulate design guidelines to account for PEF hazard to structures in seismic zones. Keywords. post-earthquake fire hazards, conflagration, performance-based design, structural strengthening, monitoring, simulation.