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Supporting steel silos on discrete, eccentric brackets offers an attractive alternative to using traditional ring beam supports in terms of both cost and simplicity of construction. A range of silos of typical geometries are analysed and the structural behaviour presented. Collapse modes are found to include buckling, plastic collapse and combined mechanisms. The results of a finite element parametric study that considers the effects of bracket width, bracket height and geometric imperfections are then presented. It is found that the strength of bracket-supported silos is strongly but non-linearly dependent on bracket width. Increasing the bracket height also increases the silo strength. Bracket-supported silos are found to be generally imperfection insensitive. However, a weld imperfection placed above the bracket can result is significantly increased strength.

Granular solids storage containers such as silos are often discharged by gravity and so need a hopper with access space beneath. Where the silo is discharged into vehicles or conveyors, the clear space must be extensive and so most silos are supported on columns. Large silos generally require a heavy ring beam (Fig. 1) to redistribute the local forces from the columns into the silo shell. This design is expensive to construct and smaller steel silos can be built successfully with a much cheaper arrangement in which the columns support brackets attached to the side of the silo (Fig. 1 and Fig. 2). While such designs are often used, their strength has never been thoroughly investigated by researchers and the limitations on their usage have only been discovered through in-service failures. There is considerable scope to extend the use of these very cost-effective support arrangements to larger structures if the mechanisms of failure can be identified and the strengths of brackets of different proportions determined.Most previous work on column-supported silos has assumed that the columns are located directly under the mid-surface of the silo wall and do not, therefore, produce moments in the wall. Teng and Rotter [1] reported the results of bifurcation and non-linear analyses of a silo supported on rigid columns performed using the finite element program, LUSAS. The study was restricted to a single shell geometry with a varying number of column supports. They extended their earlier work to include the effects of flexible column supports using linear bifurcation analyses [2]. In addition, they analysed the effects of changing various parameters such as the silo radius to thickness ratio, the boundary conditions at the top and bottom of the silo and the number and width of the column supports. Their results indicate that within practical limits, the number and width of the supports have little effect on the buckling strength of silos. Flexible supports were found to significantly decrease the buckling strength of the silo. Greiner and Guggenberger [3] reported a series of analyses on column-supported silos using the Abaqus [4] finite element code. The analyses were aimed at determining the effects of internal pressure on the strength of column-supported silos and found that this was beneficial to the stability, even at high values of pressure. More recently, Guggenberger et al. [5] described a very detailed study of the behaviour of column supported cylinders, again using Abaqus. The effects of many different parameters were investigated including shell geometry, material non-linearity, geometric non-linearity, initial imperfections and boundary conditions. The authors were sufficiently confident of their results to propose a number of design recommendations for column supported silos. Few publications have given any consideration the effect of eccentric brackets. In 1974 Gould and Sen [6] derived a simple algebraic expression for the moment transmitted to the wall of a tank by eccentric brackets. The present study takes as its starting point recent work by Gillie et al. [7] who presented a small scale study of eccentrically supported silos and highlighted the effects of both geometric and material non-linearity on their strength. This study considers first the behaviour of silos with equally spaced support brackets of typical dimensions. A series of analyses is presented which examine the effects of varying the silo r/t ratio, a number of possible failure mechanisms are identified and analytical expressions are developed to predict the collapse strength of these silos. With this structural understanding in place, the effects of varying the number and locations of supports and of geometrical imperfections are investigated.

The structural behaviour of silos supported on discrete, eccentric brackets has been studied and the effects of a variety of parameters determined. Silos with large r/t ratios were found to fail by elastic buckling and those with small r/t ratios by plastic collapse. Interaction between these two mechanisms governed the strength of silos with intermediate r/t ratios. It was also found that geometric non-linearity meant the practical strength of relatively slender silos with large bracket eccentricites was governed by serviceability criteria. Increasing either the bracket width (2d) or bracket height (h) was found to result in increased strength, although the relationship between bracket height and silo strength was weak. Bracket supported silos were found to be largely insensitve to eigenmode imperfections and to weld imperfections distant from the bracket. The effect of a weld imperfection located immediately above the bracket was found to result in significantly increased strength.