The performance of steel structures at elevated temperature is determined by many factors. This report describes the analytical investigation of a single span steel beam using the nonlinear finite element program, SAFIR. Four support conditions and additional axial spring were used to model structural elements with various level of axial and flexural restraint. Different fires were applied and the effect of the applied load, number of fire-exposed sides and location of the line of support were analysed in terms of the midspan deflection, bending moment distribution and axial force in the axially restraint beams. It was found that beams with axial restraint, especially those with rotational restraint are very sensitive to the stress-strain relationship of the steel at elevated temperatures. This research is intended to be a preliminary study leading to the detailed behaviour of complex steel frames such as those tested at Cardington. Some important aspects that could not be included in this project need further investigation in future research.