Elastic failure of locally supported silos with U-shaped longitudinal stiffeners

Abstract

For practical considerations, thin-walled steel silos are often supported by a limited number of discrete equidistant supports around their circumference. In such cases, large loads are transferred to the limited number of supports, causing locally high axial compressive stress concentrations. A possible solution is to add a partial-height U-shaped longitudinal stiffener above each support. Such stiffeners create a more gradual transmission of vertical loads to the supports, increasing the maximum failure load. This paper aims to map the influence of the dimensions of such longitudinal stiffeners on the failure behaviour of a thin-walled silo. Both the parameters of the cross-section and the height of the stiffeners are discussed. All the results and the findings are based on geometrically and material nonlinear analyses — GMNA — performed with finite element software. The simulations indicate that, in general, thin-walled silos will fail by pure elastic buckling in the unstiffened silo wall above the terminations of the longitudinal stiffeners. However, this is only true if the cross-section of the stiffeners, and to a lesser degree the moment of inertia, is sufficiently large in order that the longitudinal stiffeners can absorb the supporting loads. In contrast, for longitudinal stiffeners with a small cross-section, the silo structure will fail by premature elasto-plastic collapse of the stiffeners itself at significantly lower load levels. Furthermore, the height of the stiffeners and the degree of support - the circumferential width of the supports and the stiffeners is equal to each other — are the most important geometrical parameters which are beneficial to reach a maximum load level for a specific silo. Finally, the buckling behaviour and the failure load are hardly influenced by radial width and the thickness of the longitudinal stiffeners.