A numerical study of large deflection behaviour of restrained steel beams at elevated temperatures

Abstract This paper presents the results of a numerical study, using ABAQUS, of the large deflection behaviour of steel beams at elevated temperatures with different elastic axial and rotational restraints at the ends. A particular emphasis of this paper is the behaviour of axially restrained steel beams in catenary action. Although studies in the area of structural fire engineering has moved beyond the consideration of isolated elements to structural interactions in complete frames, catenary action in steel beams is an important aspect of structural interactions and is receiving considerable attention from researchers. After validating the capability of ABAQUS against available experimental results of fire tests on restrained steel beams, this paper describes the results of a numerical parametric study. The parameters investigated include beam span, uniform and non-uniform temperature distributions, different levels of applied load, different levels of axial and rotational spring stiffness at the beam ends and the effect of lateral torsional buckling. It is concluded that the large deflection behaviour of steel beams can significantly affect their survival temperature in fire. Indeed, if a realistic amount of axial restraint stiffness is available at the beam ends and fire engineering design is not concerned with the amount of large deflection in a beam, it is possible that the beam can have virtually unlimited survival temperature. Clearly, fire engineering design will need to consider the effect of axial forces in the beam on the adjacent structure, including the connections.