Imperfection sensitivity of locally supported cylindrical silos subjected to uniform axial compression

For the prediction of the real failure load of shell structures, such as locally supported cylindrical steel silos under axial compression, it is convenient to take into account imperfections. It is assumed that such silos are very sensitive to a wide range of (even small) geometric imperfections, and that they lower the failure load significantly. Furthermore, these imperfections caused by the fabrication or the manufacturing process, are the dominant factor in the discrepancy between the theoretical/numerical predictions based on a perfect geometry and the experimental results of an imperfect geometry. In other words, it is important to make a well-considered choice for an imperfection when predicting the real failure load. However, the imperfection sensitivity depends, among other things, on the shape of the shell, the stiffening configuration, the boundary and loading conditions, etc. Before proceeding to the calculation of interaction curves and the development of new design rules for imperfect barrels, it is essential to perform an extensive study to examine the influence of imperfections to the failure behaviour and to choose a sufficiently detrimental imperfection shape.

In this study, different imperfection forms are numerically investigated: the linear bifurcation mode, the non-linear buckling mode, several post-buckling deformed shapes of the perfect shell, and a weld depression type A and B. Additional aspects, such as the orientation, the amplitude of the equivalent imperfection, and the position of the influence of the weld depression are also investigated. The present study takes into account the European normative documents and the guidelines of the recommendations of the ECCS.