Numerical investigation on the influence of imperfections in the lateral-torsional buckling of beams with slender I-shaped welded sections

In this paper, a numerical investigation is carried out for determining the influence of imperfections on the lateral-torsional buckling of welded I-shaped slender section beams. The buckling resistance of unrestrained beams is calculated with nonlinear shell-element based FE analysis, including material and geometrical imperfections. The sensitivity to global and plate imperfections, as well as residual stresses, is presented for different amplitudes and shapes of geometrical imperfections and distributions of residual stresses available in the literature. The recommendations outlined in this work shall help the choice of these parameters on future numerical simulations and extend the observations of other authors in the context of studies for beams with non-slender sections. The comparison of the numerical results with the predictions of the North American design code, AISC360-16, and the European design code, Eurocode 3, suggests that the AISC360-16 provides an upper limit for the beam's resistance and the Eurocode 3 a lower bound, mainly because residual stresses have a greater impact in the load-carrying capacity on the studied beams. Thus, these findings are expected to promote future developments and amendments to said design codes. Finally, this investigation also supports the need of more realistic definition of imperfections, especially for the case of residual stresses, and justifies a more comprehensive experimental campaign on the subject.