Simulation of the effect of non-uniform temperatures on a beam of high strength steel within a fire compartment

In this paper, finite element (FE) models are created to simulate the response of a restrained floor-beam selected from a benchmark test subjected to heating and cooling stages in fire. After the validation of the FE models using the non-uniform thermal response and the mechanical response from the test, the most efficient model is selected to study the behaviour of beams made of both mild steel and high strength steel (HSS) under different fire scenarios. The results indicate that end-restraints of the beams and non-uniform distribution of temperature developed in beams are together the critical factors affecting the beam behaviour. Compared to mild steel beams under similar conditions, HSS beams with larger reserved strength have higher fire resistance but the beam with lower reserved strength loses its bending capacity earlier due to instability. Thereafter, the higher tension force developed in the beam can affect the behaviour of adjacent columns and connections. The studies on beams under both fast and slow fires show that the fire duration is also a key factor affecting the structural fire resistance. The methods developed in this paper highlight the importance of performance-based fire-safety design approach in designing other types of steel members subjected to non-uniform temperatures.