Finite element modelling of behaviours of steel beams and connections in fire

A three-dimensional mathematical model has been developed to simulate the response of steel structures in the event of a fire. The model using isoparametric shell finite elements is based on a tangential stiffness approach which allows sophisticated simulations to be executed economically. The model includes the consideration of the material plasticity and deterioration with temperature, non-uniform thermal expansion across a section and large deformations at very high temperatures. Analyses are undertaken using time steps. This allows the complete account of stress history of the structure, especially when the rate of temperature rise differs in different parts of the structure, Comparisons are made with the test data obtained from real fire tests on both steel beams with different support and loading conditions, and with beam-to-column connections. Both the simulated deflection-time curve and fire resistance period are found to be in good agreement with the rest evidence.