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.

Potential Impact:
The most significant impact that civil engineering research can have is to change the legally mandatory standards that are used internationally in the design of the built environment. All European Standards (Eurocodes) have a direct impact on the economic activity, infrastructure, built environment and societal development in the UK. As a result, any efficiency savings in steel use and construction brought about by more efficient design rules as a result of the proposed research will scale up to be of direct and significant benefit to UK industry and commerce. Additionally, it is important for the prestige and competitiveness of the UK academic community to be at the forefront of standards development, especially when it is backed by high-quality home-grown fundamental research. The Applicant is in a unique position to maximise the probability of this envisaged impact, as detailed in the Pathways to Impact document submitted as part of this proposal.