Imperfection effects on the buckling of hydrostatically loaded cylinders

The presence of geometric and other imperfections in cylinders has been known to result in collapse loads well below those predicted from eigenvalue analysis for a long time. As the designer's ability to routinely employ non-linear FEA has increased, the importance of modelling such imperfections in design has also increased. Practical guidance on how to do this is fairly limited, in particular for geometries or load conditions other than the standard cases. The effect of imperfections on the collapse load of cylinders under axial load has been studied extensively, as such cylinders show the largest imperfection sensitivity.Work on cylinders with other loading conditions, such as hydrostatic loading, is more limited. Similarly, there is limited work on cylinders with boundary conditions other than simply-supported ends. This paper looks at the case of cylinders under hydrostatic load, which is often important in the design of subsea structures and the case of a clamped-free boundary condition combination which is relevant to the design of offshore wind turbine foundations. A number of different methods of applying imperfections are considered and compared to the results obtained from available experimental data and standard design codes