Analysis of silo supporting ring beams resting on discrete supports

Abstract

Elevated cylindrical metal silos are often supported on a ring beam which rests on discrete column supports. The ring beam plays an important role in redistributing the majority of the discrete forces from the column supports into a more uniform stress state in the cylindrical wall, which is necessary to reduce the potential for buckling of the shell wall.Traditional design treatments assumed that the discrete support forces can be fully redistributed by the ring beam, producing circumferentially uniform axial membrane stresses in the silo shell. But it has previously been shown that only a very stiff ring beam can produce even relatively uniform axial membrane stresses in the shell. The ring beam stiffness must be evaluated relative to the stiffness of the silo shell in compatible deformation, since even a thin shell is extremely stiff in its own plane. A test for the ring beam to shell stiffness ratio was previously devised by the authors to determine the ring beam stiffness needed to achieve uniform membrane stresses. This new study assesses ring beams of practical dimensions and stiffness, to evaluate their effectiveness in smoothing the shell axial membrane stresses towards the uniform condition and then to find their effect on the buckling resistance of the shell.This study explores the stress resultants in a closed section ring beam of practical dimensions that is less stiff than the ideal stiffness using a finite element parametric study of the flexible ring beam and connected silo shell. The results show that the ring beam stress resultants, relative to those in an isolated ring beam under the same loading, can be directly related to the established shell to ring beam stiffness ratio (ψ). This treatment may be used to significantly enhance current design practice which, according to the Eurocode EN 1993-4-1 for silos, assumes that the shell applies the full uniform transverse loading onto an isolated ring beam.