Influence of the cross section slenderness on the buckling behaviour of steel welded tapered beam-column

摘要

Pitched roof portal frames are often made of welded plate elements with tapered web classifiedrnas class 3 (semi-compact) and 4 (elastic) according to EN 1993-1-1. Moreover the class of flange, with constantrnvariation along the element, can range from class 2 (compact) to class 3(semi-compact), function of their width tornthickness ratio. Under gravitational load, that is the dominant case in design practice, these elements are mainlyrnsubjected to combined action of bending moment and axial compression force. Hence the tapering of the elementsrnis made in accordance with internal force distribution under gravitational loads. Due to their cross section classrntype, the failure in buckling can be of different types. When class 2 and 3 sections, are restrained against lateralrnand/or torsional buckling, the coupling between sectional plastic buckling and overall in plane buckling of thernmembers in compression and/or in bending is possible. When class 4 (slender) sections are used, which generallyrnis the case of the rafter at the maximum height of the tapered web, the sectional buckling (e.g. local bucklingrnof walls or distortion) may occur in the elastic domain. If no lateral restrains, or when they are not effectivernenough, the lateral torsional mode could characterize the global behaviour of the frame members, or interactionrnwith sectional buckling modes may occur as well. The paper presents the results obtained experimentally, alongrnwith FEM analyses and a parametric study results. The failure mechanism, and hence the ultimate capacity isrnmainly influenced by the cross sectional and/or overall slenderness as well as the applied lateral restraints.