Buckling of circular steel silos subject to code-specified eccentric discharge pressures

It is well known that the eccentric discharge of bulk solids from silos can lead to pressure asymmetry which may have serious structural consequences. For steel silos, such pressure asymmetry is likely to lead to high local axial compressive stresses and consequently buckling failures of the silo. In existing silo loading codes, the pressure changes due to discharge eccentricity are represented by local pressure increases (or reductions) which are commonly referred to as patch loads, as the complexity of real eccentric discharge pressures has not been well understood. In general, the specification of patch loads to represent the effect of real eccentric discharge pressures has been done without a rigorous assessment of their structural consequences. The aim of this paper is to present the results of a finite element investigation into the buckling strengths of steel silos subject to code-specified pressures for eccentric discharge. The study shows that although the patch loads specified in these codes vary greatly from one code to another and may have a great effect on the linear bifurcation load, their effect on buckling loads determined using more sophisticated buckling analyses with the effect of geometric non-linearity taken into account is small. Instead, the axisymmetric primary wall loads are shown to control the buckling loads. It can thus be concluded that the patch loads specified in existing silo loading codes are inadequate in representing the effect of discharge eccentricity if this effect is important in reality, when the specified loads are used in a non-linear buckling analysis. If this effect is as small as shown by the non-linear buckling loads presented in this paper, then this effect can be easily covered by a small increase in the primary wall loads which represents a much simpler approach.