09 Nov UW-Madison engineers apply award-winning technology to road building
Madison, Wis. – Motorists driving along the DeNeveu Creek bridge on Highway 151 near Fond du Lac will never notice the difference as they drive over a bridge that uses a new method of construction developed at UW-Madison.
However, highway officials who concern themselves with the cost of road construction may definitely notice the difference in the form of a much longer-lasting road.
Instead of having a roadbed reinforced with a grid of steel bars, the bridge features a prefabricated Fiber-Reinforced Polymer (FRP) grid. The new technique was developed in a four-year project by UW-Madison engineering professors Michael Oliva and Lawrence Bank, plus two former graduate students David Jacobson and Mack Conachen. The team recently won Popular Science magazine’s “Best of What’s New” award in engineering for their work.
FRP technology itself is not new, having been used to make surfaces such as decks on oil platforms. The leap in this case comes from an expanded use of the technology. Whereas the decks on the oil platforms have a tight grid spacing of only an inch, fit for people to walk upon, the team realized that a redesign of the structure would give it a new use.
“We said, why not increase that spacing, maybe to four or six inches?” said Oliva. “And now we’ve got a rectangular FRP grid system that looks a lot like the steel reinforcing bar grids that are built inside of bridge decks.”
In economic terms, there are tradeoffs between steel bars and FRP; the manufacturing process for FRP can be up to 10 times as expensive as steel bars. On the other hand, the ability to prefabricate the reinforcement grids and lay them down quickly—as opposed to having a team of workers individually lay down steel bars and tie them together—means a bridge roadbed that takes two weeks to lay down might take two days. All in all, Oliva estimates that the costs for an FRP system would only be about 30-40% higher than steel bars after contractors become accustomed to the new system.
That greater expense could itself be cancelled out, however, by the great longevity of the bridge. After about a dozen years, the steel bars in a conventional bridge start to corrode from water and salt seeping through. Even after repairs are made, the bars have to be replaced after about 25 years. FRP material, on the other hand, is rustproof and therefore unaffected by those environmental forces. A bridge constructed from FRP could therefore last up to twice as long as a conventional bridge, more than making up for the increased up-front costs.
How long might it be it be until massive projects on the scale of the Golden Gate or George Washington bridges could see FRP technology? While still in its infancy, work is proceeding on a small bridge in Missouri as well as being promted on the West Coast. All that remains is to streamline the manufacturing and construction methods, and for public sector buyers to make the tradeoff of up-front costs in exchange for a longer lifespan, Oliva says.
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