Experimental studies of the behaviour of unprotected steel frames in fire

The deformation behaviour of unprotected steel framed structures exposed to real fire conditions has been studied experimentally and theoretically. A total of three tests on steel frames under different load level and differe nt heating process are conducted, all the tested frames are single span and single story. In order to simulate a real fire condition, heating is attai ned by a specially built gas furnace. Behaviour of each tested frame in fir e is described and comparisons are made between fire test results and resul ts calculated by a 2D finite element computer program-NASFAF developed in t he paper. The secant stiffness matrix which relating the total element disp lacements to the corresponding total element nodal forces is used in develo ping the program and the effects of geometrical non-linearity, "softening" of material at elevated temperature, gradual penetration of inelastic zone both along and across each member, non-uniform distribution of temperature are all taken into consideration. Creep effect is considered in an approxim ate way in the temperature-dependent stress-strain curves of the material. (C) 1999 Elsevier Science Ltd. All rights reserved.