The load carrying behaviour of cylindrical thin-walled shell structures under axial load is strongly dependent on imperfections invariably caused by manufacturing processes. Axisymmetric imperfections have been recognised to result in particularly severe reductions in strength. Imperfections in the vicinity of circumferential welds in steel silos and tanks fall into this category and therefore deserve special attention. Finite element models were used to analyse imperfect cylindrical shells and special care was taken to model the weld-induced circumferential imperfection. The geometry was calibrated against data gained from measuring such imperfections on existing silos and residual stresses were taken into account. Interaction between neighbouring weld imperfections and the role of the strake height in this interaction was investigated. Residual stresses were found to increase the buckling load. The extent of this increase proved to be dependent on various parameters such as weld geometry, weld depth and strake length. The buckling and post-buckling behaviour of imperfect structures either with or without residual stresses was studied in close detail. This study enabled the mechanism leading to the strengthening effect of the residual stresses to be clearly identified.
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