Response of Asymmetric Slim Floor Beams in Parametric-Fires

State-of-the-art slim floor systems are a 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 the material strength as a composite beam. It also offers a larger area to support the steel decking and pre-cast slab units during the construction of floor. Experimental and analytical investigations on response of asymmetric slim floor beams have shown that these beams offer a higher fire resistance in comparison to the conventional composite systems with down-stand steel beams. Previous investigations on these beams have been conducted in standard fire exposure conditions, hence, their response to natural fire scenarios still deems further examination. This study addresses 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 obtained show that the asymmetric slim floor beams behave differently in parametric-fires in comparison to that in standard fire exposure conditions. Asymmetric slim floor beams continued to support the loads for the whole duration of parametric fires without undergoing excessive deflections and offering a better fire resistance. Unlike in case of the standard fire where the temperatures keep on increasing throughout the duration, 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 beams 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. Deflections predicted for the beams were found to be directly related to these average temperatures. 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

Effect of Air-Gap on Performance of Fabricated Slim Floor Beams in Fire

Fabricated slim floor beams are produced by welding a steel plate to the bottom flange of an I-shaped steel section. The welded steel plate makes them structurally efficient and serves as a platform to support the steel decking of composite floor and the pre-cast concrete slabs. During their fabrication, an air-gap is induced between the steel plate and the bottom flange. Previous experimental investigations have shown that this air-gap has an influence on their thermal behaviour at elevated temperatures. Though the air-gap presence has an influence on their thermal performance, no investigations have yet been conducted to analyse its effects on their structural response in fire. This research investigates the effects of air-gap on structural response of fabricated slim floor beams in fire. During this study, finite element modelling is performed to simulate the response of fabricated slim floor beams and the predicted behaviour is verified against the available test data from literature. The validated finite element model is then employed to perform parametric studies to investigate the effects of the presence and size of the air-gap on their response in fire. Results obtained show that the presence of the air-gap has a significant influence on structural response of these beams at elevated temperatures. On the other hand, the size of air-gap has no or negligible effect on their thermal behaviour as well as on their structural response in fire. It was found that the presence of the air-gap restricts temperatures on the bottom flange and helps in achieving an improved fire resistance. As the presence of the air-gap is found to be helpful and beneficial, findings from this research can be used to develop similar designs for structural members as an efficient and inexpensive way to improve their behaviour in fire