In Refugio County, Texas, salty coastal air and brackish water combine with a moist subtropical climate and 37 inches of rain per year to create a highly corrosive environment for steel and other traditional building materials. When Haas-Anderson Construction was chosen to replace an old wood and steel drainage ditch bridge on FM1684 near Tivoli, TxDOT saw it as an opportunity to further testing of fiber reinforced polymer (FRP) beams.
Armando Bosquez, Transportation Engineer in TxDOT's Corpus Christi District, says that "TxDOT annually has funds for innovative research projects, and we look for ideal locations to try newer technologies. In this case, the location is suitable because of the low volume of traffic and its proximity to the coast. The coastal environment promotes corrosion, and the FRP beams aren't susceptible to corrosion. The bridge was already going to be replaced and the FRP option was chosen."
The beams installed on the Tivoli Bridge are a set of eight 50-foot-long custom FRP flanged U-Shaped Beams produced by the Molded Fiber Glass Construction Products' Texas plant. Each FRP beam weighs approximately 5,000 pounds and rests upon concrete abutments under a conventional poured concrete deck. All concrete, columns and bridge decking were supplied by Alamo Concrete Products, Ltd., and are reinforced with steel provided by CMC.
When the FRP beams are compared to concrete, they are very lightweight, and a dozen can be delivered on one truck. "The FRP beams are similar to a large concrete pipe in weight and delivery methods," according to TxDOT's Armando Bosquez, and "The main difference is size and weight. The FRP beams occupy less space and are lighter. They are easier to handle and place. Also, the long term cost/benefit ratio should be better than conventional steel and concrete, if the beam's longevity is as expected."
The Tivoli bridge, completed in September 2007, is the second application of FRP beams in Texas, the first having been installed in San Patricio County three years ago. Despite initial concerns about creep or sag, load testing over a period of two years demonstrated the durability of the FRP beams and has revealed no unexpected problems. TxDOT expects to use more FRP beams in the future, and manufacturers eventually want to offer standardized FRP beam designs rather than having to custom build beams for each individual bridge. Additionally, fiberglass-reinforced polymer may be incorporated into bridge decking, and manufacturers are hoping to make it feasible for more widespread applications.