Influence of web imperfections in welded I-beams with slender webs

The study is devoted to the influence of apparent initial out-of-flatness together with residual stresses in the typical case of welded I-beams in bending. The theoretical model is a portion of an I-girder, analysed by means of a nonlinear FEM package. A simple approach is used to account for the postcritical response of the slender web to the initial compression due to welding. A parametric study is carried out on the combined influence of both the initial geometrical imperfections and residual stresses on the "stub-beam" bending capacity. Some contradictory trends in the effects of the two factors are found to interact, thus leading to a favourable balance. The results demonstrate that the design procedure of EC3 - due to its empirical origin - covers a high level of imperfections. Therefore even large out-of-flatness has no practical influence and thus no theoretical justification may be found for keeping more severe and restrictive tolerances in practice.