Improvement of the prediction of the flexural buckling resistance of hot-rolled mild and high-strength steel members

The determination of the bearing capacity of a member under compression, presenting an initial out-of-straightness and residual stresses resulting from the production process, is a stability problem governed by the geometry of the member and the mechanical properties of its constitutive material. Amongst these, the yield strength plays a key role. Indeed, it has a direct impact on the spread of yielding in the member but, also, the detrimental effect of geometrical and material imperfections decreases as the yield strength increases. The effect of these initial imperfections is considered by an imperfection factor α in the design recommendations provided in EN1993–1-1. However, the current and new upcoming versions of this norm give a stepwise evolution of this imperfection as a function of yield strength by only distinguishing grades lower than S460 from the ones equal/higher than S460. The present paper aims to briefly summarize the existing studies on this topic, to assess the recommendations of current and new upcoming versions of EN1993–1-1 and the models reported in the literature and, finally, to suggest a modified imperfection factor for hot-rolled sections (H-shape and I-shape) for already existing grades (up to S500) but also for grades up to S690, which do not exist yet for this section typology in the European steel market, to evaluate the structural benefit of developing them.