An Assessment of the Eurocode 3 Provisions for Lateral-Torsional Buckling of I-Sections under Uniaxial and Biaxial Bending

In this paper, the two-node geometrically exact beam finite element proposed by the author (Goncalves 2019) is employed to assess the current Eurocode 3 (CEN, 2005) provisions for I-section beams undergoing lateral-torsional buckling and subjected to uniaxial or biaxial bending.

For uniaxial bending, the beam finite element is used to determine (i) elastic non-linear bifurcation loads (i.e., accounting for pre-buckling deflections), (ii) large displacement elastic post-buckling paths including geometric imperfection effects and (iii) large displacement elastoplastic equilibrium paths accounting for geometric imperfections and residual stresses. Three support/loading cases are considered: (i) simply supported beams under uniform moment, (ii) simply supported beams subjected to a mid-span vertical force and (iii) cantilevers subjected to a free end vertical force. Besides I-sections with standard height-to-width ratios, wider flange sections are also considered, and it is demonstrated that, for the latter, the post-buckling behavior is quite different from that of standard sections and an increase in the load carrying capacity is observed, which is not predicted by the current Eurocode 3 provisions. Based on the results obtained, a set of recommendations are given.

For biaxial bending, standard I and H sections are considered and three support/loading cases are also examined: (i) simply supported beams under uniform moments, (ii) beams simply supported at one end and fixed at the other, subjected to end moments, and (iii) cantilevers subjected to free end forces. lt is demonstrated that the Eurocode 3 provisions can provide very conservative estimates of the collapse load and a proposal for their improvement is provided.

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