Procedure 9-6 Design of Bins and Elevated Tanks

The definition of a bulk storage container can be quite subjective. The terms bunkers, hoppers, and bins are commonly used. This procedure is written specifically for cylindrical containers of liquid or bulk material with or without small internal pressures. 

There is no set of standards that primarily applies to bins and since they are rarely designed for pressures greater than 15 psi, they do not require code stamps. They can, however, be designed, constructed, and inspected in accordance with certain sections of the AS ME Code or combinations of codes. 

When determining the structural requirements for bins, the horizontal and vertical force components on the bin walls must be computed. A simple but generally incorrect design method is to assume that the bin is filled with a fluid of the same density as the actual contents and then calculate the equivalent hydrostatic pressures. While this is correct for liquids, it is wrong for solid materials. All solid materials tend to bridge or arch, and this arch creates two force components on the bin walls. 

The vertical component on the bin wall reduces the weight load on the material below, and pressures do not build up with the depth as much as in the case of liquids. Consequently, the hoop stresses caused by granular or powdered solids are much lower than for liquids of the same density. However, friction between the shell wall and the granular material can cause high longitudinal loads and even longimdinal buckling. These loads must be carefully considered in the case of a deep bin.  

In a shallow bin, the contents will be entirely supported by the bin bottom. In a deep bin or silo, the support will be shared, partly by the bottom and partly by the bin walls due to friction and arching of material. 

---