Over the past several years, there has been a resurgence of interest in studying the response of building structures to fires. Simulations of the effects of severe fires on the structural integrity of buildings requires a close coupling between the gas phase energy release and transport phenomena and the stress analysis in the load bearing materials. A methodology has been developed for coupling CFD simulations of fire growth with finite element models for thermal analysis and for using the

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... mal data to compute the demand-to-capacity ratio in a multi-story structure. A simple radiative transport model that assumes the compartment is divided locally into a hot, soot laden upper layer and a cool, relatively clear lower layer is employed to predict radiative fluxes incident on sub-grid scale structural members. Thermal response coupled with realistic fire simulations of various steel structural components on floors of World Trade Center Tower 1 that were subjected to aircraft impact damage and fires are presented. The thermal response was used to compute the reduction in load carrying capacity of the structural components as a function of time, which ultimately results in global collapse of the towers.