Computational Analysis of Steel Joists at Elevated Temperatures

Steel joists are economical and efficient structural assemblies usually designed to transfer the load imposed on roofs or floor decks to structural frames. In many applications, steel joists are required to provide fire resistance for a given interval; therefore, they are either protected by fire-resistant membranes (e.g. ceiling) or fire-resistant materials (e.g. intumescent coating). Currently, the amount of time a steel joist is able to withstand the effects of fire (i.e. fire rating) is determined experimentally by testing conventional steel joist configurations subjected to a standard time-temperature curve known as the ASTM E119 standard fire. In the current design methods for building construction, a designer selects steel joist assemblies and finds complete design requirements based on the assemblies. Using this method, designers have a relatively limited number of options to choose from. Additionally, fire ratings are assigned based on data gathered during experiments in laboratory settings that barely represent the actual loading and support conditions experienced by steel joists in a building. Consequently, it is impossible to accurately estimate the actual performance of these steel assemblies beyond the dimensions of the furnace, and at elevated temperatures produced by real fires different than the ASTM E119 standard fire. This research project explores the possibility of effectively analyzing the behavior of steel joists at elevated temperatures using advanced computational tools. It focuses on developing computational models of common steel joists subjected to elevated temperatures due to fire. Numerical results are validated against experimental results available in the literature, and the models are assessed as potential alternatives to standardized fire tests