The strength of thin-walled cylindrical shell structures is highly dependent on the nature and magnitude of imperfections. Most importantly, circumferential imperfections have been reported to have an especially detrimental effect on the buckling resistance of these shells under axial load. Due to the manufacturing techniques commonly used during the erection of steel silos and tanks, specific types of imperfections are introduced into these structures, among them circumferential weld-induced imperfections between strakes of steel plates. The main objective of this thesis was to investigate the exact nature of these circumferential welds and their influence on the buckling resistance of silos and tanks under axial load. The results of a survey of imperfections in existing silos at a location in Port Kembla / Australia (Ding 1992) were used to develop and calibrate a shape function which accurately describes the geometric features of circumferential weld imperfections. It was found that after filtering out the effects of overall imperfections, three parameters governed the shape of the surveyed imperfections: the depth; the wave length; and the roundness. A study on several factors influencing the buckling of silos and tanks was carried out using the finite element method. The interaction between neighbouring circumferential weld imperfections was investigated and it was found that the influence on the buckling behaviour depended on the strake height in relation to the linear meridional bending half wave length and the depth of the imperfection. The strengthening effect of weld-induced residual stress fields for a range of different geometries was also studied, and diagrams were derived giving the influence of the newly developed shape function on the buckling behaviour. A post-buckling analysis was undertaken and a model for the post-buckling behaviour of cylindrical thin-walled shells with circumferential weld imperfections was developed. The methods used for the analysis of thin-walled cylinders were applied in a study on the buckling behaviour of welded box-sections. It was found that weld-induced residual stress fields governed the buckling behaviour of these columns / Doctor of Philosophy (PhD)