Buckling behaviour of circular cylindrical steel shells under basic load cases

Cylindrical shells exhibit one of the most efficient forms of structural members. Due to this high structural efficiency and high material performance of steel, it is generally feasible to design and construct (very) thin-walled shell structures capable of supporting massive loads. For this reason, metal shell structures are used in diverse applications such as wind turbine towers, tanks, silos, pipelines, offshore platforms, chimneys, pressure vessels, cooling towers and aerospace launch vehicles. Because of this wide range of application, there are different actions, e.g. axial compression caused by the structure’s self-weight, external pressure generated by wind loading and shear produced by seismic actions, occurring during the service life of a shell structure and causing various failures. The most common failure mode for a shell system or a part (e.g. segment, strake) of a shell structure, however, is buckling, which is characterised by sudden large displacements due to the loss of stability under compressive membrane or shear membrane stresses in the shell wall. Despite a high structural efficiency and a wide application range of cylindrical shells made of steel, it is difficult to predict the buckling strength of a shell structure. This difficulty is due to the high sensitivity of the buckling strength to initial geometric (material) imperfections, boundary conditions and geometric (material) nonlinearity. Hence, it is almost very challenging to provide safe and economic design rules that consider all impacting factors and are applicable to each shell structure. Different codes, standards and guidelines have attempted to specify rules for the buckling design of thin-walled shell structures. The European Standard on the Strength and Stability of Metal Shells EN 1993-1-6, however, was the first worldwide to allow the benefits of advanced nonlinear analysis to be taken to produce generalised rules for the buckling design of all shell structures. Nevertheless, the algebraic expressions in Annex D of EN 1993-1-6 have been derived almost as lower bounds of buckling test results without including the advantages of advanced computational analyses. For this reason, within the frame of this thesis, a comprehensive numerical investigation into the linear and nonlinear buckling response of perfect and imperfect cylindrical shells under fundamental loading conditions – i.e. axial compression, external pressure, torsion – was conducted. Based on the results of finite element analyses, new expressions were devised for the buckling capacity parameters of cylindrical shells under the above load cases, leading to an accurate estimation of the buckling strength and thus economic design. Theoretical, numerical and experimental results collected from the literature were then used to assess the reliability of numerical outcomes and the applicability of the proposed design approaches. Stainless steels exhibit a rounded stress-strain response, with no sharply-defined yield stress. As this material nonlinearity can have noticeable effects on the buckling strength of medium-slender and stocky cylinders, new design approaches have been proposed herein, leading to accurate resistance predictions for stainless steel shells.