摘要：Single storey industrial buildings with steel structure composed by portal frames disposed in parallel constitute a very frequent kind of construction. The computational simulation of steel structures under fire conditions is usually performed by the twodimensional finite element analysis of the structure. In this way the analysis of the behaviour of single storey industrial buildings is performed either by the simulation in the plane of the steel portal frame or, simply the roof truss. However, the two-dimensional analysis takes into account neither the out-of-plane instabilities, nor the out-of-plane redistribution of efforts. These effects can play an important role in the structural performance of a building in a real fire situation. In this paper a comparative study of two- and three-dimensional models of a portal frame industrial building under elevated temperatures is presented. The importance of the out-ofplane effects and the adequacy of the plane model to represent the real behaviour is discussed. The computer program SAFIR5 , developed at University of Liege for analysis of structures submitted to fire, was used in all the simulations. Amongst other features, the structural analysis performed by SAFIR considers: the effects of large displacements; the non-linear variation of material properties with the temperature; the effect of the thermal elongations; the evolution of the structural behaviour given as a function of time (an automatic time step can be used).
