Bulletin

March - April 2007, Vol. 73, No. 2

Tech-Bytes

Lighter Bridge Decks Working

Workers install a fiber-reinforced
polymer deck

There’s an innovative material showing up on bridge decks around Virginia. Fiber-reinforced polymer (FRP) composites, a substance used for decades by the marine and aerospace industries, may allow some bridges to be built better, lighter and ultimately more efficiently.

VDOT recently installed three FRP bridge decks—on two replacement bridges over Canton Creek on Tangier Island and on the restored Hawthorne Street Bridge in Covington—and the results look promising. These installations followed a temporary test site at the I-81 Troutville weigh station, which was studied for several years beginning in 1999 by the Virginia Transportation Research Council and Virginia Tech.

FRP composites blend resins, additives and fillers with a reinforcing agent such as glass or carbon fibers. Its initial fabrication costs are higher than steel’s, but its longer life and lower maintenance costs can outweigh the initial expense.

FRP bridge decks are also lighter than concrete decks. The new deck on the Hawthorne Street Bridge, which reopened in December 2006, weighs about 25 pounds per square foot, or about 75 percent less than a comparable concrete deck. Weight was a key factor on this bridge because of its history and location in Covington. The 75-foot-long steel-truss bridge over a rail line was built in the late 1800s and is eligible for inclusion on the National Register of Historic Places, but corrosion and other deterioration had rendered it potentially unsafe for vehicle or pedestrian traffic.

Before it closed, the old bridge had a seven-ton load rating; now it can withstand 20 tons. Because of issues with intersections on either end of the bridge (road grade, alignment, right of way), VDOT could not build a new bridge that would meet current federal standards – thus its decision, at the request of the city, to rehabilitate the current bridge within its existing physical restraints. Reopening the Hawthorne Street Bridge in the center of town also means emergency vehicles no longer rely on underpasses elsewhere that are prone to flooding.

The new deck is composed of a series of square fiber-reinforced polymer tubes that are adhered side by side and sandwiched between FRP plates to form a hollow deck panel. Each panel is about five inches thick and is as strong as a conventional concrete deck but weighs much less.

The Tangier Island bridges, also installed in 2006, replaced two timber-decked bridges with hollow FRP deck systems. The old structures were deteriorating from exposure to the elements and were difficult to maintain. Because Tangier Island has no infrastructure for road maintenance, using corrosion-resistant materials such as FRP on the bridge decks will reduce the long-term costs of transporting crews, equipment and materials from the mainland.

Virginia and other states also have incorporated FRP materials as superstructure elements or reinforcement in the support systems of various bridges as well as in bridge decks. The Federal Highway Administration (FHWA) reports that the United States has more bridges using FRP composites than any other country.

FHWA has also supported many of these projects through its Innovative Bridge Research and Construction (IBRC) program. The Research Council, on behalf of VDOT, has received more than $1 million in these IBRC grants in three consecutive funding cycles for this research. Virginia is the only state to have accomplished this.

Dr. Michael C. Brown, P.E., who coordinated the grant requests for VTRC, oversaw the studies by Virginia Tech’s Virginia Cooperative Center for Bridge Engineering for both the Tangier Island and Hawthorne Street bridge projects. He said these projects could not have been implemented without the efforts of the Hampton Roads and Staunton districts and adds that such collaborations by VTRC and Virginia Tech will allow VDOT to pursue more innovative technologies that will benefit motorists.

— by Ann Overton

Page last modified: Wednesday, January 16, 2008