March 29, 2003
Many older highway structures throughout the United States are in need of repair or replacement, and Tulane researchers are in the forefront of developing new and practical replacements for this aging infrastructure.
Paul Ziehl, assistant professor of civil and environmental engineering, has completed testing a representative specimen of fiber-reinforced polymer honeycomb that will be used in the construction of a New York highway bridge this summer. The specimen, installed in a fixture adjacent to the civil engineering building on the uptown campus, was subjected to a tremendous load from a pair of hydraulic rams last month, with the intent to test it to failure.
Ziehl, who specializes in fiber-reinforced polymers and their applications to civil structures, says concrete bridge decks are routinely being replaced nationwide due to corrosion of reinforcing steel and other durability issues.
"One option for replacement, instead of going back to another steel or reinforced concrete bridge, is to go with a fiber-reinforced polymer bridge," says Ziehl.
Among the advantages of this alternate material are that it is corrosion-resistant, strong and extremely lightweight, making installation easy. Fiber-reinforced polymers are composite materials typically comprising a fiber made of carbon or glass imbedded in a hardened polymer resin such as epoxy.
Possessing desirable mechanical properties that in many cases far surpass those of their constituent parts, these materials have been used in innumerable scientific, industrial and commercial applications, including aerospace and airplane structures, storage tanks, automotive components and boat hulls, and have even been used to enhance the performance of such familiar items as golf clubs and fishing rods.
For the initial testing for the New York bridge, Ziehl and his colleagues developed a computer model to predict the material's behavior in different situations. A key aspect of Ziehl's research procedures is nondestructive, acoustic emission monitoring that makes use of numerous sensors to detect cracking in a test specimen, enabling Ziehl to pinpoint areas of weakness. It was Ziehl's test expertise that swayed the New York Department of Transportation to send a prototype segment of the bridge to Tulane for evaluation.
"They wanted to have some insight into damage mechanisms as they are taking place, which a simple destructive test doesn't tell you," says Ziehl.
The honeycomb bridge structure withstood loads of 84,000 pounds at each of two loading points and still did not fail. This is 10 to 12 times the projected traffic loading on the bridge. As the technology for fiber-reinforced polymer structures matures, new and more daring engineering applications for the material beckon.
"The most promising application for fiber-reinforced polymers may be in very, very long span bridges where weight is a critical issue," says Ziehl. A typical concrete deck weighs about 100 pounds per square foot, and a fiber-reinforced polymer deck can be from 20 to 30 pounds per square foot.
"On a long-span bridge like the Golden Gate Bridge," says Ziehl, "the majority of the load is due to the weight of the bridge itself--the weight of the traffic is much less significant. So if you use a fiber-reinforced polymer deck and girder system and carbon fiber cables, you have really cut down on the weight."
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