Steel silos with different aspect ratios: I — Behaviour under concentric discharge

The current European standards for the design of thin-walled metal silos require the designer to use a complex combination of rules covering many different aspects of loading, structural behaviour and strength. Each individual rule was often developed autonomously, usually with implicit and undocumented conservative assumptions. When combined, the overall factor of safety of a designed silo may be significantly different from that guaranteed by the standard, making it difficult to reproduce the design rules in a numerical calculation that does not include the same implicit assumptions.This paper explores the behaviour of five thin-walled cylindrical silos with stepwise-varying wall thickness and aspect ratios varying from very squat to very slender, all custom-designed for and analysed under the EN 1991–4 concentric discharge loading condition. The aspect ratio plays a deciding role in both the behaviour and design of silos, and it is important to ascertain that a finding that is valid for one is transferable to the others. The nonlinear finite element analyses reveal that the computed load factor exceeds the partial safety factor in design by a large factor over a wide range of aspect ratio, suggesting that the overall design process is particularly conservative. The reasons for these discrepancies are explored.This paper is the first of a pair. The second paper explores the behaviour of the same set of example silos under the EN 1991–4 eccentric discharge loads, with fundamentally different conclusions.

Research highlights
► Eurocode-designed metal silos show high buckling strengths under symmetrical loads.
► Many undocumented conservative assumptions inherent to silo-relevant Eurocode norms.
► Large discrepancies between codified and numerical buckling strength predictions.
► Important nonlinear effects in buckling of metal silos not considered by the Eurocode.