Numerical investigation of the lateral–torsional buckling of beams with slender cross sections for the case of fire

• Numerical investigation of LTB of slender cross-section beams for the case of fire.
• The influence of several parameters is analysed through a parametric study.
• An effective section factor is proposed to account for local-overall interaction.
• Development of a LTB proposal for the fire design of studied beams.

An extensive numerical study is performed to investigate the lateral–torsional buckling of steel beams with slender cross sections for the case of fire. The influence of local buckling is analysed, and the numerical results are compared to the simplified design methods of Part 1-2 of Eurocode 3 for the case of beams with Class 1 and 2 cross sections. The actual provisions of Eurocode 3 Part 1-2 are demonstrated to be unreliable. A parametric study is carried out to investigate the influence of several parameters on the resistance of laterally unrestrained steel beams with slender cross sections for the case of fire: the effective section factor, temperature, steel grade, depth-to-width ratio (h/b) and residual stresses. Based on the parametric study, a proposal for a new design curve is made for beams with slender cross sections for the case of fire, taking into account the influence of local buckling by grouping the response of beams into different ranges of effective section factors. The capacity predicted by the simplified methods using the proposed design curve leads to an improved yet safe design method compared to the results of the finite element analysis.