A Model for Post-Earthquake Fire Spread Considering Structural Damage of Buildings Caused by Seismic Motion and Its Progression Due to Heating of Fire

Abstract

A physics-based model for post-earthquake fire spread was developed by modifying the prototype model previously proposed by the authors. In the new model, seismic motion and heating of fire are both considered as the causes of damage upon building members. The damage results in the change of fire behavior for individual building and criteria for building-to-building ignition. Indices representing the structural damage of a building are as follow: inclination angle of columns; falling ratio of exterior claddings; and deficit ratio of partitioning walls. Charring of wooden column gradually reduces its bearing capacity along with the decrease in its area of cross section. This may yield buckling of the column as well as collapse of the entire building. As to the falling of exterior claddings and burn-through of partitioning walls, the rates of degradation are assumed to be proportional to the cumulative heat flux received by the building members. The falling of exterior claddings increases the probability of ignition due to external heating, and the burn-through of partitioning walls allows transfer of heat and mass between neighboring rooms. For the verification of the new model, simulation of fire spread which followed 1995 Kobe Earthquake was conducted. Behavior of fire spread obtained by the numerical simulation was compared with the survey data at which reasonable agreement was obtained.