Response of Bare Steel Members Exposed to Localized Fire Hazards

摘要

The current structural fire design practice is developed for post-flashover fires and is based on a maximum temperature method which assumes that: if the maximum temperatures in a structure or member subjected to design fires do not exceed a limit temperature (which is usually determined by a standard fire test), the structure or member is regarded to have sufficient fire resistance and to be able to survive the design fires. The maximum temperature method may be conservative for the case where the failure of the structure or member is caused by the loss of strength, but may be not conservative if the failure is caused by the loss of stability (due to the "P-delta" effect caused by thermal gradient, for example). This paper discusses responses of bare steel members exposed to localized fire hazards. Some recent studies on the thermal calculation and structural response of bare steel members exposed to localized fires are presented. Simple models are provided to predict the temperature of exposed members in a localized fire. Sequentially coupled thermo-mechanical simulations were performed to investigate the failure mode of bare steel members. The study found that because of the effect of thermal gradient, a bare steel component may fail in a totally different way in a localized fire than in a standard fire, and the failure temperature for a steel component in a localized fire might be hundreds of degree lower than that in a standard fire.