Parametric analysis of the lateral–torsional buckling resistance of steel beams in case of fire

Abstract

Numerical modelling of the lateral-torsional buckling of steel beams at elevated temperature has shown that the beam design curve from EN 1993-1-2 is over-conservative in the case of non-uniform bending. Based on the newly proposed methodology for cold design from the EN 1993-1-1, an improved proposal for the lateraltorsional buckling of unrestrained steel beams subjected to fire is presented in this paper that addresses the issue of the influence of the loading type, the steel grade, the pattern of the residual stresses (hot-rolled or welded sections) and the ratio h/b, between the depth h and the width b of the cross-section on the resistance of the beam, achieving better agreement with the numerical behaviour while maintaining safety. The proposal is found to be safe and accurate through an extensive comparison with the results of FEM numerical simulations of more than 5000 beams. A statistical study of the results is performed, showing the accuracy of the improved proposal presented in this paper.

Response of steel beam–columns exposed to fire

“…Vila Real et al [5][6][7] studied the LTB resistance of steel beams under standard fire exposure by investigating the effect of initial imperfections, residual stresses, and the yield strength of steel. Based on experimental and numerical studies, they proposed modifications to the Eurocode LTB design equations to account for the faster degradation of the elastic modulus of steel, as compared to its yield strength, at high temperature.…”

Lateral–torsional buckling of stainless steel I-beams in case of fire

“…The authors have made a new proposal for the lateral-torsional buckling of carbon steel beam elements in case of fire [14] that adopts, following EN 1993-1-1 [13], a modified reduction factor for the lateral-torsional buckling χ LT ,fi,mod , given by…”

“…For welded sections the severity factor is given in Table 2 [14]. The effect of this severity factor is to move the beam design curve in the vertical direction placing it closer to the numerical points.…”

“…Based on the proposal made by the authors [14] for lateral-torsional buckling of carbon steel beams, described in the previous section, similar numerical studies of stainless steel beams subjected to high temperatures, were made. These studies also resulted in the proposal of Eqs.…”

“…These new proposals [14,15] follow the same approach as in part 1.1 of Eurocode 3, also taking into consideration the influence of the loading type.…”