Lateral-distortional buckling of composite cantilevers

摘要

Composite steel-concrete tee-beams cantilevered from a fixed root and subjected to gravity loading are a form of composite construction in which the entire steel I-section is subjected to a combination of negative bending and compression. Under such loading, the steel component is subjected to lateral-distortional buckling, since the top flange is restrained by the concrete slab. This paper considers the elastic buckling of composite cantilevers, which represents a grey area in design against structural instability. Hitherto, design methods such as the well-known inverted U-frame approach have been applied to this problem, in lieu of the extremely conservative assumption of treating the problem as one of lateral-torsional buckling. A well-publicised finite element method of analysis is applied to the problem, and the behaviour of a specific cross-section cantilever beam is considered. In particular, the buckling mode shapes are considered, as is the positioning of a lateral brace within the span that prevents the transverse and twist buckling displacements of the bottom flange.