Over the past several years, there has been a resurgence of interest in studying the response of building structures to fires. Typically, the thermal loading for structural analysis of a building subject to fire is obtained from a standard time-temperature curve or by assuming a spatially uniform enclosure temperature. This decouples the structural analysis from the fire simulations and as a result the structural response to spatially and temporally evolving fires cannot be predicted. 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 and structural analysis. 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 responses for 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. One of the most striking observations that emerges from these results is the wide variation of time-temperature curves at different points in the structure and the lack of resemblance of these curves to the standard time-temperature curve used in furnace tests of structural elements. The thermal response was used to compute the reduction in load carrying capacity of the structural components as a function of time.
Citation: Fire Safety Journal
Pub Type: Journals