Local and distortional buckling of extruded aluminium alloy lipped angle columns

The outstand flanges of aluminium alloy angles are sensitive to local buckling due to the low elastic modulus of material. To improve the sectional buckling stress, lips could be introduced to improve the stability behaviour of the outstand flanges. This paper presents an equilibrium approach and a simplified energy method for the local and distortional buckling of extruded aluminium alloy lipped angle columns. Closed form solutions for local buckling and distortional buckling are proposed. The equivalent flexural rigidity and torsional rigidity of the lip are two main factors affecting the sectional buckling behaviour. As distinct from double-sided symmetrical edge stiffeners, the bending of a single-sided edge stiffener can lead to in-plane compressive deformation of the adjacent flange. Based on the edge-stiffened flange model, the equivalent flexural rigidity of the lip is obtained from finite element (FE) analysis. To validate the proposed analytical methods, the elastic buckling coefficients of lipped angles with varying dimensions are obtained from eigenvalue buckling analysis. Lips of different thicknesses are considered to study the effect of torsional rigidity. Comparing with FE results, the proposed equilibrium approach shows excellent accuracy for both local and distortional buckling stresses. The closed form solution given by energy method can also well predict the sectional buckling stress. Finally, parametric studies are carried out to further investigate the effects of flexural and torsional rigidities of lips and the slenderness ratios of flanges on the elastic buckling behaviour. Some design remarks are concluded to provide valuable reference for the application of extruded aluminium alloy lipped angles in practice.