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 components. The damage affects burning behavior of a fire involved building as well as behavior of building-to-building fire spread. For validation 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 observed data. Reasonable agreement was obtained with regard to the number of burnt buildings.KEYWORDS: post-earthquake fire, urban fire, fire spread, physics-based model, Kobe city.
NOMENCLATURE LISTING
The prototype model previously developed by the authors was improved in order to simulate the behavior of fire spread in an earthquake-affected urban area. In the new model, seismic motion and heating by fire are both considered as the causes of damage to building components. The damage affects the burning behavior of a fire-involved building, as well as the behavior of building-to-building fire spread. For validation of the new model, a simulation of the fire spread that followed 1995 Kobe earthquake was conducted. The behavior of the fire spread obtained by the numerical simulation was compared with the observed data. Reasonable agreement was obtained with regard to the number of burned buildings.
Taniguchi, et al. [1] developed an analytical method for evaluating the absolute maximum elasto-plastic displacements of multi-degree-of-freedom (MDOF) oscillators under the action of base excitation based on a modal combination. Its essence is that 1) modal frequencies, shapes and damping during yielding of any member of the MDOF oscillators are readily specified by the modal analysis with the secondary stiffness of the members being yielded, 2) assuming that a bilinear hysteresis may describe the force-displacement relationship of each mode, an equivalently linearized system consisting of a single-degree-of-freedom (SDOF) oscillator is introduced to approximate the absolute maximum elasto-plastic displacement of each mode, 3) the absolute maximum elasto-plastic displacement of the MDOF oscillator is evaluated by the Square Root of Sum of Squares rule (SRSS-rule) by combining the maximum elasto-plastic displacement of each mode approximated by the proposed equivalently linearized system. This study first provides small modification in the equivalently linearized system. Then, employing a couple of MDOF oscillators whose spring at arbitrary storey may yield and an accelerogram, the maximum elasto-plastic displacement of the MDOF oscillator is calculated by the proposed method and is compared with that computed by the time history analysis. Their comparison suggests that the proposed method can reasonably evaluate the absolute maximum elasto-plastic displacement of the MDOF oscillator subjected to earthquake excitation as the conventional SRSS-rule does that for the linear MDOF oscillators.
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.
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