Studies of the behaviour of steel beams in fire

Abstract A series of results calculated using the secant stiffness method is presented for the structural behaviour of simple steel floor beams in fire. The influence of a number of parameters is considered. The importance of the shielding effect of concrete floor slabs, observed in tests, is confirmed. However, the sensitivity of failure temperatures to the magnitude of the temperature difference between the top and bottom flanges is shown to be relatively small. The moment capacity method of BS5950 predicts failure temperatures fairly accurately and conservatively. The support conditions have a considerable effect on survival, with greater fixity resulting in improved behaviour even when the higher design loadings are taken into account. Beams with different spans and cross-sectional depths but identical span/depth ratios are shown to have virtually identical failure temperatures, which decrease as the span/depth increases. Other aspects for which results are presented are the possibility of enhancing beam behaviour by using asymmetric cross-sections or reducing design loads, and the heating of individual spans within continuous beams.