Bill Wilcke, Minnesota Extension Engineer
Because grain storage space was tight last fall, a number of farmers used concrete stave silos, which are normally used for silage, haylage, or high-moisture corn, to store surplus grain. Silos can work quite well for storing grain, but grain managers should be aware that outward pressure against silo walls, especially during unloading, is much greater for dry grain than it is for other crops. This outward pressure can cause spectacular failures of silos that can lead to loss of grain, property, and potentially, human life.
The first step in preventing silo failure is to make sure that the silo is adequately reinforced. Since the joints between concrete staves don’t provide much resistance to the outward pressure exerted by stored crops, steel hoops are usually installed around the outside of concrete stave silos to reinforce them. Pressure is greatest at the bottom of the silo, so more hoops (smaller spacings between hoops) are used near the bottom. Pressure is also greater for crops like dry grain that flow easily, so concrete stave silos that will be filled with dry grain should have more hoops than silos that are designed only for silage. Check with the silo manufacturer to determine the proper hoop spacing for dry grain. If the silo is filled to no more than 15 ft from the top with dry grain, however, the pressure is comparable to that for a full depth of silage and additional hoops might not be needed.
The next step in preventing silo failure is to make sure that the hoops are in good condition and that they are properly fastened and tightened. Check hoops for signs of excessive corrosion from silo acids, for cracks in any welded joints, and for drooping out of position, which would indicate that they aren’t tight enough. Contact a silo company if you need help with the inspection or with hoop maintenance.
Finally, use great care when unloading dry grain from silos. Unload the silo from the bottom-center to avoid creating the uneven stresses that would occur with side unloading. Also, since outward pressures can increase during unloading, unload the first half of the silo slowly to avoid excessive pressures. And keep a close watch on the hoops during unloading. If you see or hear hoops breaking, or see staves bulging out, get away from the silo immediately!
This page is part of the Biosystems and Agricultural Engineering Department web at http://www.bae.umn.edu/