ELASTIC DISTORTIONAL BUCKLING OF TAPERED COMPOSITE BEAMS

The overall buckling mode in a composite steel-concrete beam over an i nternal support is necessarily lateral-distortional, in which the bott om compressive range displaces laterally and twists, since the top fla nge is restrained by the nearly rigid concrete slab. An efficient fini te element method is used to study elastic lateral-distortional buckli ng in composite beams whose steel portion is tapered. The simplified m odel for a continuous beam that is presented herein is a fixed ended c antilever whose steel portion is tapered, and is subjected to moment g radient, This is intended to give an insight into distortion in a cont inuous beam that occurs in the negative bending region, and the differ ences between the cantilever representation and the continuous beam ar e highlighted. An eigenproblem is established, and the buckling modes and loads are determined in the elastic range of structural response. It is found from the finite element study that the buckling moment may be enhanced significantly by using a vertical stiffener in the region where the lateral movement of the bottom range is greatest. This enha ncement is quantified in the paper.