A study of cylindrical shells under global bending in the elastic‐plastic range

Many thin cylindrical shells are used in structural applications in which the dominant loading condition is global bending. Key examples are chimneys, wind turbine towers, tubular piles and tall silos. These structures are generally much thinner than pipelines and tubular structural members, but are often much thicker than the highly imperfection-sensitive, very thin shells used in tanks and squatter silos. Their thickness lies in an uncomfortable range which is extremely thin for the structural tube community and very thick for the shell buckling community. The buckling strength of these structures is dominated by extensive plasticity, but the fully plastic state is usually far from being attained. There has been much controversy over the appropriate definition of strengths for these shells in the last few years, caused by the mismatch between design rules used by different communities and attempts to harmonise all rules into a single generic description. This paper explores the buckling strength of imperfect thin cylindrical shells under bending in this elastic-plastic range, and shows how the capacity curve of the new Eurocode EN 1993-1-6 (2007) can be used to express the behaviour accurately and safely. It is assumed that the shell is held circular by rings or boundaries at reasonable intervals, effectively restraining ovalisation. It is hoped that these results will make a useful contribution towards resolving the misunderstandings and controversy that has been evident in this field in recent times.