Numerical modelling of the fire resistance of steel I-beams with restrained thermal enlogation

In this paper the influence of the restrained thermal elongation in the behaviour of steel I— beams being part of a frame has been studied. In fact there is a significant difference between the case of a beam acting as a single element free lo exhibit axial thermal elongation or being pan of a frame where the stiffness of the remaining strucure contributes with some restraint to the free elongation of the beam. A numerical study of the behaviour of steel I-beams subjected to fire and a combination of axial force and bending moments has been presented. A geometrical and material non-linear finite element program, specially established at the University of Liège for the analysis of structures submitted to fire, has been used to determine the resistance of a beam-column at elevated temperature, using the material properties of Eurocode 3. part 1-2. The numerical results have been compared with those obtained with the Eurocode 3, part 1-2 (1995) and the new version of the same Eurocode (2002). The results have confirmed that the new proposal for Eurocode 3 (2002) is more conservative than the ENV-EC3 (1995) approach