Two ninth grade school boys, Martin Chin and Paul Trainer did this bridge project. The boys performed all construction. Mr. Bosch took a hands off approach, providing only guidance, tools, and a garage to build it in. The finished beams weighed only 65 pounds each and were made of balsa wood and fiberglass.
The photos above show the finished beams being held overhead by the students. A Cadillac Eldorado was then driven onto them, loading them to over 5,000 pounds (including decking). The students had reached their goal at this point but their teacher now insisted that they be tested to failure, so a Mack truck was driven onto them. Mr. Bosch was told that the truck weighed 12,000 pounds, which crushed the balsa wood core (the beams were designed to hold an Eldorado, not a Mack truck -- intermittent use of pine in the core probably would have held the truck since it got almost 1/2 of the way across before failure). This just goes to show that you can break anything if you pile enough weight on it.
Mr. Bosch later got his hands on an engineering paper filled with formulas "proving" that these beams could not even support a Motorcycle. The paper was based on the erroneous assumption that the core experiences shear loads, when in fact these loads are taken up by the skin (see the How It Works section for more details).
Mr. Bosch had arranged for the beams to be tested before the public at the Stanford Shopping Center in California, but at the last minute the Shopping Center backed out. This created a big problem since Mr. Bosch had already arranged for various media representatives to witness the demonstration. The demonstration was then shifted to a Los Altos lumberyard, which was willing to host the test. When the test finally took place, the only media representative was a photographer from The Mercury newspaper of San Jose California (no reporters bothered to show up). This photographer later went out of his way to inform Mr. Bosch that the article was going to be a negative one. Sure enough, for some reason The Mercury newspaper of San Jose printed an extremely negative article.
Eighteen years later (1986) Mr. Bosch located Martin Chin (one of the students). At this point Martin gave Mr. Bosch a technical report on the Captive Column that he had written while he was a junior in high school. Martin had abandoned his goal to become an engineer and went into medicine instead.
Copyright © 1998-2004 by Lawrence R. Bosch.