A high-performance, carbon fiber-reinforced polymeric material recently applied to an overpass bridge in metro Atlanta is one of the first such applications of its kind in the nation. The reinforcement is expected to strengthen and extend the life of the bridge.
The rehabilitation of the bridge is part of a research project funded by the Georgia Department of Transportation (GDOT) in cooperation with the Federal Highway Administration (FHWA). Researchers at the Georgia Institute of Technology are conducting the research.
The Lee Road bridge over Interstate 20 in Douglas County suffers from cracks in its concrete deck. A research team led by Dr. Abdul-Hamid Zureick, a professor in Georgia Tech's School of Civil and Environmental Engineering, hopes that strips of fiber-reinforced polymeric (FRP) material will extend the bridge's life at least five to 10 years. They are monitoring the bridge closely to gather durability data.
"We are taking an integrated field/laboratory approach," Zureick said. "We lack sufficient guidelines for engineers, contractors and the GDOT regarding the use of these new materials. We need information about safe construction procedures, GDOT design guidelines and bidding documents. They are the keys for the success of this technology."
Indeed a future goal of Zureick's research is to generate national guidelines, which could be used in FRP structure repair projects worldwide, he said. Such documentation could be in place within two to three years.
The need for repair guidelines stems from the widespread problem of substandard bridges — those that are structurally deficient and/or functionally obsolete. The Federal Highway Administration's (FHWA) 1996 Better Roads Bridge Inventory indicates that about 31 percent of the nation's bridges are substandard.
Several factors contribute to the problem. They include: aging bridges (about half were built before 1940); shorter durability because of airborne pollutants (carbonation) and de-icing salts (corrosion); increasing daily traffic; increasing truck weights; more frequent vehicle overloads; and insufficient repair funds.
"Traditional repair and replacement of bridge components, including bridge decks, pile caps and pre-stressed concrete beams, is very expensive," Zureick said. "But with high-performance, fiber- reinforced polymeric composites technology, repairs can be made very fast, and that cuts costs in the long term."
In fact, the Lee Road bridge repair took workers less than a day to complete what could have taken several weeks to do traditionally, Zureick said.
With time and money at stake for highway departments nationwide, Zureick's team has been working intensely since their study began in early 1996. This work builds upon an extensive experimental and analytical research program assessing the strength of FRP for use in new construction and in structure rehabilitation since 1986. Now the research team — which includes Drs. Roberto Leon and Lawrence Kahn from the Georgia Tech School of Civil and Environmental Engineering, as well as several students — are simultaneously conducting laboratory and field tests on FRP materials.
So far, laboratory tests have determined that FRP materials can make bridges 30 to 40 percent stronger than the original design. They are gathering long-term data and plan to estimate the benefits over a bridge's lifespan once all data are analyzed.
"Fibers possess tremendous strength. And you can lay the fibers in any pattern you want to accomplish the strength you need," Zureick said.
Additional FRP material laboratory tests conducted in an environmental chamber are addressing every potential aspect of bridge component behavior during the structure's lifespan, expected to be 75 years under current design criteria. Researchers are exposing components to extreme conditions, including humidity, temperature, salt and ultraviolet light. They will incorporate the durability data they collect into predictive models that will estimate FRP bridge component lifespan, Zureick said.
Meanwhile, Georgia Tech researchers are assessing the condition of three Georgia bridges, including the Lee Road structure, that were selected by GDOT for FRP material tests. The other two bridges being tested are in Murray County near Dalton, Ga., and near St. Simons Island.
GDOT contractors using sheets of carbon fiber-reinforced material repaired pile caps on the Murray County bridge in just four days in the spring of 1997. Zureick's research team is now monitoring the material's performance, which is quite good so far, he said.
"Ease of installation is a definite advantage of fiber-reinforced materials," Zureick said. Workers use any of several available adhesives to apply readily available, but initially expensive FRP materials to bridge components. "It's kind of like pasting on wallpaper," Zureick said. In fact, it is about as lightweight as wallpaper. Two different types of FRP materials used on the Murray County bridge weigh 2 and 5 ounces a square foot — only a fraction of the weight of traditional steel plates used for bridge repair, he added. This factor also makes installation easier and faster.
While the potential is great for use of FRP materials in bridge rehabilitation, Zureick said, the key question is its durability. FRP materials have been used successfully in aircraft construction, and FRP material has been used to repair bridges in Switzerland for more than six years.
Meanwhile, Zureick and his co-investigators are training a large number of undergraduate and graduate engineering students in the use of FRP technology. "It is exciting that the next generation of engineers will have an alternative material for construction and repair," Zureick said.
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