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Time Line - 1972: Coal Mine Crib Beam... |
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The Captive Column Coal
Mine Beam ready to get squeezed to
one million pounds. (101k) |
This Coal Mine Crib Beam used a Modified Captive Column design. A
spaced core (a core with gaps) was used in this Captive Column, which the inventor rarely
used because it is less efficient. However, the Captive Column Company made this
particular beam, and their reasons for making this beam with a spaced core are vague. The
Captive Column Company was one of the inventors first licensees and went out of business
after this photo was taken. The history of the Captive Column Company is a chapter in
itself and will be covered at a later date.
Mr. Bosch did not make this beam so the material used for the core elements is unknown,
but it looks like aluminum in some old photos. Here are the recorded characteristics for
the Coal Mine Crib Beam:
| Length: |
5 feet. |
| Depth: |
~ 18 inches. |
| Cross Section: |
Equilateral triangle. |
| Materials: |
Aluminum (?) core, fiberglass columns and skin. |
| Weight: |
200 pounds (40 pounds per foot). |
| Load: |
1,000,000 (one million) pounds. |
| Deflection: |
None. |
The strength-to-weight ratio of this beam was 5,000 (1,000,000 / 200). One of the
reasons that this beam could take such a heavy load was that its slenderness ratio was
relatively low (5 feet long and 18 inches deep) when compared to Captive Columns
tested in the past. In addition, Captive Columns are most efficient when loaded on end.
This was a particularly heavy Captive Column due to the loading requirements. This beam
was designed to replace the extremely heavy wood logs used to prop up coal mine tunnels.
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