Capacity Reduction and Fire Load Factors for Design of Steel Members Exposed to Fire

A general reliability-based methodology is proposed for developing capacity reduction and fire load factors for design of steel members exposed to fire. The effect of active fire protection systems (e.g., sprinklers, smoke and heat detectors, fire brigade, etc.) in reducing the probability of occurrence of a severe fire is included. The design parameters that significantly affect the fire design of steel members are chosen as random variables. Raw experimental data published in the literature was analyzed to obtain the statistics of parameters for which no statistical information was available in the literature. Model errors associated with the thermal analysis models are also characterized based on experimental data. It is found that uncertainty associated with the fire design parameters is significantly higher than that of room temperature design parameters. To illustrate the proposed methodology, capacity reduction and fire load factors are developed for simply supported steel beams in U.S. office buildings, and it is shown that for consistent reliability these factors should vary depending on the presence of active fire protection systems in a building.