Response of Asymmetric Slim Floor Beams in Parametric Fires

State-of-the-art slim floor systems are the newest addition to the composite construction industry and several types are currently being used for building and construction purposes. Asymmetric slim floor beams are a type of slim floor systems which consist of a rolled section with a larger bottom flange. The larger bottom flange induces asymmetry and offers an efficient use of material strength as a composite beam. It also offers a larger area to support the steel decking and pre-cast slab units during construction of the floor. Experimental and analytical investigations on the response of asymmetric slim floor beams have shown that these beams offer a higher fire resistance in comparison to the conventional composite systems with the down-stand steel beams. Previous investigations are conducted in standard fire exposure conditions, hence, their response to natural fire scenarios still deems further examination. This study addresses the response of asymmetric slim floor beams in natural fire exposure conditions. For this purpose, finite element models developed and verified by the authors are employed to study the thermal and structural response of slim floor beams in fast and slow parametric-fire exposures. Results show that asymmetric slim floor beams behave differently in parametric-fires in comparison to that in standard fires. The asymmetric slim floor beams continued to support the loads for the whole duration of the parametric fires without undergoing excessive deflections and offering a better fire resistance. Unlike in case of the standard fires where the temperatures keep on increasing throughout their duration, the temperatures on the slim floor beams decrease after reaching a maximum point in parametric fires. It was found that for fast parametric-fires, the thermal gradient across the section is more severe as compared to that for the slow parametric-fires at earlier stages of fire exposure. In case of the fast parametric-fires, the rise and fall of temperatures on the slim floor beam are rapid while in case of the slow parametric-fire, these variations in temperatures are subtle. It was observed that the structural response of slim floor beams in standard and parametric fires depends on the average temperature across the steel section. The deflections predicted for the beams were found to be directly related to these average temperatures. The outcomes of this study will benefit in understanding the response of asymmetric slim floor beams in natural fire conditions and will aid to develop simple fire design methods for future use.