Horizontal saddle-supported storage vessels: Theoretical and experimental comparisons of plastic collapse loads

Previous experimental work (1) on cylindrical vessels supported at the ends and subjected to central loading indicated that different collapse mechanisms could occur when the loading is applied either through loosely fitted saddles or through welded saddles. The modes of failure are dependent upon the value of the R/t ratio of the vessel. In general, progressive plastic collapse occurs in vessels with low values of R/t ratio, typically less than 200, and elastic-plastic buckling is observed in vessels with higher R/t ratios. The aim of this paper is to examine various theoretical analyses for plastic collapse loads, applicable to vessels with low values of R/t ratio, and compare these with the experimental results obtained by the authors and others. The theoretical behaviour appropriate for the thinner vessels, where the mode is failure is by buckling, has been previously examined by the authors elsewhere (2) although all the experimental values are included here for completeness. A number of classical and numerical analytical methods are employed to obtain the plastic collapse loads. Comparisons with the experimental results show that the elastic-plastic finite element analysis gives the best agreement. Further work in the form of a parametric study has been conducted on a range of vessels to enable a design method to be established. This is published as a companion paper in this volume.