Time: 12 years
Prototype | | | | | Product
Last November, John Hillman stood beneath a bridge built with prototype plastic-and-concrete beams of his own design. Then he signaled for his team to release a nine-million-pound coal train. "You can do all the calculations you want; you can do tons of lab testing. But at the end of the day, you run a heavy-axle coal train over the bridge, and that pretty much tells you whether or not it's gonna hold," Hillman says. It didn't budge.
The concrete in a standard bridge beam absorbs vertical pressure, called compression, while the steel is tremendously resistant to tension, the force of the beams being stretched between columns. As a structural engineer, Hillman knew that arches are the ideal shape for resisting compression. So he figured he could create a stronger, lighter beam by simply casting the concrete in the shape of a four-inch-thick arch rather than a solid column. A strip of steel across the bottom of the arch absorbs tension, and a shell made from fiber-reinforced plastic and shaped like a traditional beam adds strength and corrosion-resistance.
In 2000, Hillman patented his idea and received a $340,000 federal grant to bring it to life. Along with $160,000 from composite and steel suppliers, he had enough to build a prototype. He approached Dennis Mertz, a bridge expert at the University of Delaware, who liked the idea so much that he offered Hillman access to the university's manufacturing and test facilities. Then Hillman began the years-long process of testing steels and composites and perfecting the beam's manufacturing.
The beam he's created can handle 3.5 times its load limit before giving way (the standard target is around 2.5). And it weighs about 3,300 pounds before the concrete arch is poured onsite—a tenth the weight of a conventional beam, so it's cheaper to ship. Even with the arch in place, it's a third as heavy, so crews can install it with lighter-duty cranes. Hillman estimates that the beam could save 15 percent on the cost of a bridge.
By the end of this year, drivers will be crossing two new bridges built with Hillman's beams, a 58-foot span in Chicago and a 31-footer in New Jersey. Hillman will probably stand underneath that one as well, just to reassure himself. "Even to this day, I always have doubts that it works," he says. "As a bridge designer, you're not allowed even one failure."
More Invention Awards:
A special Thanks to the guys at Elliot Co. of Indianapolis for the special plastic they manufacture for this project!!!
I find this invention to be a great key for mass transportation. Now that the gasoline crisis is upon us we will have to seriously think on using alternative ways to move about instead of driving our vehicles. A way to do it would be to start building Monorail Systems that would take us to our destinations on above grade level beams. Such as the ones mentioned in this article.
I worked with John in 87 on a segmental cable stayed bridge north of Richmond Va. He had passed his EIT and the project was a finishing school of sorts. John was looking towards new technologies way back then but was also busy gaining strong design and construction experience. He had worked on other projects previously as well as through college. I lost contact with him but would hear from other friends that he was working on alternate forms of reinforcement as well as materials substitution for structural members. He used to joke that we should prove our structures the same way the russians did. By placing multiples of maximum dead load while the entire construction team from designers to labor stood under the structure. I haven't talked to John in 20 years but I'd stand under his beam and not think twice about it.
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Its good that you've really presented on how strong this bridges are. Through your pictures people would fully understand on how bridges are constructed and how they are built.