Lateral Torsional Buckling of Cellular Steel Beams

Present paper deals with the behavior of so-called cellular members against lateral torsional buckling. These beams comprising regularly-spaced web openings are especially used for their high resistance-weight ratio, the possibility to integrate service pipes within their height, and aesthetics. Such profiles usually exhibit a complex behavior, since they can experience many modes of failure, including local instability ones, i.e. those involving an out-of-plane instability of the web post at high shear locations and/or distortion of the cross-section. For what regards global instability, the members are usually designed by means of rough design rules, which often lead to an unduly conservative girder, the beams sometimes showing over 200% resistance reserve. Present research aims at improving this situation, by means of new adequate design formulae. In this respect, both experimental and extensive numerical parametric studies have been undertaken. First, a series of 3 full-scale tests has been performed, the main goal of which being the validation of purposely-derived FE models. Since the numerical models showed a very good agreement with the tests, they have been further used to gather a large set of numerical reference results where many parameters were varied: the relative slenderness, steel grades, cross-section shapes, bending moment distributions, and relative sizes of the openings. Finally, a new set of dedicated design rules has been derived, that was proved to be accurate while leading to safe estimates of the resistance when compared to all reference results.

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