Ring Beam Stiffness Criterion for Column-Supported Metal Silos

Abstract

Cylindrical metal silos are commonly elevated to provide access space beneath to directly discharge the contained materials into transportation systems. Evenly spaced column supports are commonly utilized. In larger silos, the discrete forces from supports are more evenly transferred and distributed into the cylindrical shell wall by using a ring beam. A fundamental assumption in the design of the silo shell is that the meridional compressive stresses are relatively uniformly distributed around the circumference. This assumption can easily be violated if the ring beam is flexible, so it is necessary to determine the ring stiffness needed to achieve a particular degree of uniformity of support. Current methods of assessing this stiffness rely on onerous finite-element analysis, which only provides information for the specific design being checked. In this paper, a criterion is developed to identify the required ring beam stiffness to achieve a particular degree of uniformity in the shell stresses. It is based on the ratio of the ring beam stiffness to the cylindrical shell stiffness in axial deformation in the fundamental harmonic mode of the column support, assuming that the ring is concentrically loaded and supported at equal intervals around the circumference. Vlasov’s curved beam is used to derive a closed-form solution for the ring beam stiffness and semimembrane theory for the cylindrical shell. The resulting stiffness ratio is verified using an extensive numerical study. It is shown that the method provides an effective means of determining the required stiffness of a supporting ring beam.