Non-axial stress state in a model silo generated by eccentric filling and internal inserts

Dangerous nonuniformity of grain loads within a silo may be caused by eccentric discharge, eccentric loading, eccentric structural members fastened to the wall, geometrical imperfections or nonuniformity of the frictional conditions. Some of these effects have been quantified based on testing corrugated-walled, flat floor model silos filled with wheat. In this type of silo, filling above a height to diameter ratio of H/D = 2.0 resulted in mixed flow (following the terminology of Eurocode 1) where grain slides along the wall during discharge above the effective transition and remains stagnant below the effective transition - located at H/D = ca. 0.7 (more details in [1]). The degree of load asymmetry due to eccentric filling is demonstrated and compared to the worst case observed, i.e., eccentric discharge through an orifice located at a distance of 0.7 of the floor radius from the silo centerline. The presence of a nonsymmetric flow obstruction on the silo wall is found to cause dangerous local loads similar to eccentric discharge. Considerable nonuniformity in the load is observed during testing of a cylindrical obstruction immersed in grain supported on the silo floor with its axis parallel to the silo centerline. The mechanisms of these phenomena are still poorly understood, and a satisfactory theoretical description cannot be given.