Lateral stability of slender cold-rolled hollow tubular sections with initial imperfections

Abstract

The European design code for steel structures, Eurocode 3 Part 1-1, defines the buckling resistance criterion, which enables initial imperfections to be taken into account without including them in the model structure. The initial imperfections are taken into account by the reduction factor for buckling χ. This reduction factor depends on the imperfection factor α defined in Table 6.1 of Eurocode 3 Part 1-1. Several full-scale tests have showed that initial imperfections for cold-formed hollow tubular sections, defined in Eurocode 3, are overestimated compared to the experimental results. Indeed, the initial imperfections of a cold-formed hollow tubular section are closer to the initial imperfections of the buckling curve “a” than to those of buckling curve “c”. Furthermore, a considerable difference was observed between the findings of the interaction formulae for the beam-columns in Eurocode 3, without modelling the initial imperfections, and the findings obtained with the cross-section resistance criterion, by modelling the initial imperfections. This difference is due to the buckling coefficient χ defined for a structure loaded to its full potential. To overcome this problem, a new design procedure is proposed for beam-columns without lateral-torsional buckling. This procedure involves new buckling coefficients χ* and new interaction formulae, which enable the following points to be taken into account: the intensity of the loads applied to the structure, the type of analysis (1st or 2nd order) and the required level of the criterion in line with cross-sectional properties (elastic, linear plastic or non-linear plastic).