The Captive Column pictured above was 20-feet long and weighed 65 pounds total (3.25 pounds per foot). Designed as an early prototype of a portable Troop Carrier Bridge, it triggered some interesting reactions:
There would have been two beams used for a production Troop Carrier Bridge, and the loads would have been more evenly distributed (5 wheels per beam). The pictures taken above were done at an impromptu test since the defense contractor it was built for refused to test it. Mr. Bosch later heard that the engineer that had contacted him for the beam was in fear of losing his job since he had done so without clearing it with upper management first. Seeing that the Captive Column could solve a big problem in Vietnam and save American lives, this engineer had simply tried to do the right thing by checking out a promising new technology.
The test itself was in interesting experience for Mr. Bosch. A group of curious onlookers had gathered along a fence as the test was set up. First, Mr. Bosch held the beam overhead for photos. Then the beam was staged for the tractor. Comments like "No way!", "You've got to be kidding!", and laughs were heard from the crowd as the tractor was driven into position. Their attitude changed dramatically when the tractor drove onto it.
Made of balsa wood and fiberglass, it held approximately 10,000 pounds of the 15,000-pound tractor. In spite of the flexibility of the fiberglass, the deflection was only 5 inches. Higher modulus materials such as steel or graphite would have permitted correspondingly stiffer construction.
The bottom line is this: Mr. Bosch built a 65 pound beam out of balsa wood and fiberglass that outperformed a high-strength steel I-Beam weighing over 420 pounds (NBS), or 280 pounds (U.S. Army), and he did this in his garage over 31 years ago:
Copyright © 1998-2004 by Lawrence R. Bosch.