Behaviour of tubular members and cylindrical shells under non-uniform moment gradients

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Tubular or cylindrical hollow steel members are used extensively as load-bearing members, piles, pipelines, wind turbine support towers, chimneys as well as tanks and silos. However, their treatment under bending in current design practice is surprisingly simplistic and varies between excessive conservatism and potentially serious unconservatism as a consequence of the widespread lack of understanding of the nonlinear phenomena that govern their behaviour. The effects are dominated by local buckling, strongly influenced by cross-section ovalisation, with the complexity of plasticity, post-buckling, imperfections and non-uniform load conditions. In particular, ovalisation under bending plays a critical role in reducing the buckling resistance by up to 50% in even relatively short members, but no account of it is taken in normal design. With the aid of modern computational tools and processing power, it has only recently become possible to overcome the combined complexities and make significant advances in this field. This proposal seeks to investigate numerically the nonlinear buckling behaviour of tubulars with a very wide range of lengths and thicknesses under the most commonly occurring and realistic non-uniform moment distributions. No known study has explored these effects to date, and no safe recommendations for design can be made. It is envisaged that this project will deliver a significant contribution to fundamental structural mechanics and lead to greatly improved European design guidelines, permitting substantial efficiency savings in modern steel construction in the UK and beyond.