Parametric study on distortional buckling of monosymmetric beam-columns

The paper presents a parametric study on the elastic distortional buckling of simply supported monosymmetric I-section members under a uniform moment and an axial force. Parameters describing member length and the geometry of the section are non-dimensionalised in such a way that the flange and web sizes are separated, thereby enabling clear identification of the effects on distortional buckling behaviour of the flange size, the web size and the member length. The buckling analysis is based on the Rayleigh-Ritz method with the total potential energy functional for the flanges (modelled as beam-columns) and web (modelled as a plate) derived rigorously using the fundamental strain-displacement relationships of a three-dimensional solid continuum. The reduction in the buckling moment capacity resulting from web distortion is expressed by the distortion factor, being defined as the ratio of the buckling moments with and without web distortion. Results obtained show that the effect of web distortion is more significant in members that are short, have slender webs or whose smaller flanges are in compression. A simple empirical buckling formula is proposed for predicting the moment distortion factor for monosymmetric beam-columns having equal flange thicknesses.