On the Interaction Between Local and Lateral-Torsional Buckling of I-Shaped Slender Section Beams

The work presented herein addresses the effect of local buckling on the carrying capacity of I-shaped beams with slender sections and its interaction with the lateral-torsional buckling failure mode. The use of slender I-shaped sections is particularly attractive for long-span beams where the designer profits from the bending resistance of the flanges while optimizing the web dimensions up to an extent where its main function is to provide efficient support to the flanges. However, since limited research has been undertaken on this subject, not only the safety level of existing design standards is unclear but also the influence of residual stresses, plate imperfections and global imperfections has not yet been consistently addressed for such cases. The paper studies such influence by employing material and geometrical nonlinear, shell-element based FE analysis. Different assumptions are considered in terms of the magnitude of the geometrical imperfections and distribution of residual stresses on the numerical models and the results are compared with the North American design code, AISC360-16, and the European design code, Eurocode 3. Based on the implicit assumptions of the design codes, it was found that AISC360-16 provides an upper limit for the beam's resistance and the Eurocode 3 a lower bound, mainly because residual stresses have a strong impact in the carrying capacity of the beams with slender section. This expands the observations of other authors in the context of studies of beams with non-slender sections. Hence, it is recommended that the proper characterization of these material imperfections is addressed in the future on the basis of experimental tests and, if necessary, that amendments are made to the design codes.

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