Multi-compartment silos

Whenever a conical silo is split into separate compartments, careful design calculations are required. Various design pitfalls must be avoided that can lead to asymmetric pressures imposed on internal components, given certain product, ambient and load conditions (wind, rain, snowfall, and seismic). These pressures can cause uneven emptying and further loading or pressure peaks. The silo designer must be knowledgeable regarding inserts involved in a properly constructed split or multi-sectional storage silo and their effect in relation to pressure peaks resulting from erratic flow properties. Stiffening supports and multiple openings in silo hoppers or cone bottoms must be incorporated as needed.

Other considerations are the structural ramifications of a multi-compartment silo, which may be full on one side and completely or partially empty on the other(s) under high wind loads or in severe weather conditions, such as tornado (vacuum conditions) or hurricane (severe uplift and external wind-load pressures). Even in the absence of pressure peaks due to external adverse factors, nonuniform pressures created by eccentric withdraw from multi-compartment silos can cause total structural failure. Designing a multi-compartment silo by splitting a simple, single-compartment storage tank is a recipe for potential disaster.

The same design criteria apply even more stringently to rectangular or square silos. Placing a mass-flow product like cement or fly ash into a bin-style silo that may have been designed for funnel-flow material properties — imagine how sand is drawn down — can create an underdesign situation. If mass flow develops, the pressure may be much greater than design criteria would accommodate in a funnel flow bin. Consequences could include silo collapse. While the reverse situation may occur, the ramifications are not as great. Clearly, if your storage bin or silo is designed as a rectangular structure for bulk powders, it must be fit for the storage and discharge of mass-flow products (if that is what you plan to store) and not funnel-flow products.

Temperature considerations

Observing that the belts are not running upon viewing a plant, a concrete producer may assume the plant is idle. Yet, the plant is always in motion, especially where storage silos are concerned. Silos are like huge sails when subjected to wind loads; they deflect, sway, and even rotate. However, the silo moves differently depending on how full or how empty it is at a given time. Think of the silo's movement relative to its contents as comparable to the position of the sail to the wind — the effect is that great. The variables are seemingly inexhaustible, but certainly, load combinations for wind and uplift in silos that are full, partially full, and empty are important design criteria. Empty silos, for example, are not necessarily creating lower loads.

Picture a cool evening about ten o'clock on a Saturday. A fully exposed silo (any shape) has been standing in the sun all day long. Now, consider that the plant is idle, and the silo is nearly full, having been partially filled last at two o'clock on the previous afternoon. Suddenly, a huge implosion occurs; cement (or any given powder) rains down on everything. Fortunately, all plant personnel had left the yard for the weekend.