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John's Blog

Friday, December 10, 2010

Grain silos: Form following function

The Evening Descends - 12"x 30"

You've heard the term, "form follows function"? Well grain silos are a perfect illustration of this.

Twilight's Last Gleaming - 8"x 13"
I have been fascinated with these cylindrical icons for more years than I can remember. I'm not sure why. Maybe it's the close association they have with country life, folks living off the land and helping one another...a less confused life where one works hard, produces a product that benefits people, sells that product and provides for his family. Maybe I find silos appealing because I so much enjoyed visiting my grandparent's farm while growing up...or maybe it's nothing more than the fact it's a bold, beautiful, dramatic shape that contrasts nicely with the sky and landscape. Whatever the reason, there's definitely something special about them.

Hues of Autumn - 18"x 30"
There are many ways to store farm products in bulk. Storage structures come in all shapes and sizes and can be used to store all kinds of stuff, from wood chips to cement. One way to store product is just dig a pit, dump your stuff in and cover it with a tarp. But the structure that I find most fascinating is the grain silo, more specifically, the concrete tower silo. These things were invented by Franklin Hiram King (1848-1911). They were first made of wood but these were more prone to fires, rodent infiltration and moisture than the new and improved concrete ones. There are also steel silos but I do not find them visually appealing.

Late September - 30"x 30"
Farmers have always needed a way to store large amounts of grain, seed, and even silage. Now silage is a fodder. Fodder is stuff livestock eat. It is harvested while green and usually consists of grass, alfalfa, sorghum, oats or maize. It's loaded into a silo and left to ferment. Later it can be used as feed or as biofuel.
Now the idea is, whatever you put in the silo needs to stay dry.

The Way Home - 30"x 40"
So why use a cylinder? This is where the search for a better way to do things led to the cylindrical tower...a case of function determining form.
The tower design proved to be better than square or rectangular shapes for several reasons:
  • Takes up much less space
  • More economical to build
  • Requires fewer joints since there are no corners. Only joints are at the top and foundation
  • More airtight and therefore better protected from weather, rodents, etc.
  • Design and construction is much stronger in resisting tons and tons of vertical and horizontal pressure
  • Requires much less machinery to load and unload material
  • More efficient storage shape
Some of these silos are made of cast concrete while others are constructed with concrete staves. These staves are small precast concrete blocks with ridged grooves along each edge that help lock them together. The blocks are stacked vertically with a slight stagger. All the blocks are then bound together with steel hoops encircling the tower. Since outward pressure is greatest near the bottom of the silo, the bands are more closely spaced there, with fewer bands toward the top.
The beauty of this design is that the whole thing can be disassembled and moved to another site.

The Call of Dawn - 14"x 28"
Grain silos typically range in size from 10-90 feet in diameter and 30-275 feet tall.
Material is loaded into a silo from the top by means of a conveyor, bucket elevator, chute system or a combination of these. Except in the case of silage, the material is removed through an opening at the bottom of the silo. Weight of the material and gravity alone are all that's needed to complete the process.
String a few of these silos together and you have an elevator. That's for next time.



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