SPANNING THE NEWS

There’s an easy way to recycle plastic in Sugar Grove, Va. Hop on your bike and cross over a bridge spanning Dicky Creek. When you get to the other side, cycle back.

One of the longest fiber-reinforced polymer (FRP) composite bridges was dedicated recently—fueling further development of these “plastic” structures. And, yes, cars and trucks can run back and forth, too.

The 38-ft, two-lane, clear-span bridge is supported by eight 36-in.-deep composite beams and meets U.S. standards (AASHTO HS-20) for full tractor-trailer traffic.

The project was the culmination of an Innovative Bridge Research and Construction program sponsored by the Federal Highway Administration. The major participants were VDOT headquarters personnel and VDOT District 9 engineers and construction crew, the Virginia Transportation Research Board, two engineering departments at Virginia Tech University and Strongwell Corp., Bristol, Va., which manufactured the beams.

Between 1995-1998, Strongwell researched a 36-in. double web beam with carbon fiber and top and bottom flanges for extra stiffness, then conducted testing with Virginia Tech.

“The beams are like rectangular tubes with wings on top and bottom,” Glenn Barefoot, corporate marketing manager for Strongwell, told Roads & Bridges. “This is a double-web beam, and the reason we went that way was for structural capacity and for stability. One of the things you have to deal with steel plate girders is you have to put in diaphragms or brackets every 8 ft to keep them from rolling or buckling during loading. By having a double web you eliminate that buckling effect.”

During testing, the fiber-reinforced polymer composites were over seven times the strength required in the design, and each beam was around 6.3 to 6.6 million on the modulus for elasticity.

“The Achilles heel for FRP is stiffness,” said Barefoot. “They are a great product in terms of weight and corrosion resistance. In cold weather they actually get stronger.”

Adding polymer carbon gives the beam more flexibility, but it also can loosen one’s grip on the budget. The product costs about 13 times more than steel.

“There’s a cost value problem,” said Barefoot. “Steel is a great, great product and it’s very, very cheap. Same way with concrete.”

However, steel and concrete need constant attention. Maintenance dollars are needed for both. On the other hand, FRPs jibe with the environment and are more prone to corrosion.

“Federal Highway is looking at some ways of reducing the high costs of maintaining the transportation system,” said Barefoot, who sees FRPs used for spans 50 ft or less.