CONTACT: Robert Steffen
603-862-3850
WRITER: Virginia Stuart
603-862-3102
Click for closeup of bridge, grad student Jody Trunfio (left), & Robert Steffen
UNH AND STATE BUILD NATION'S FIRST BRIDGE WITH CARBON-FIBER-REINFORCED DECK
DURHAM, N.H.--If the three little pigs had built bridges instead of houses, you might expect a bridge made with steel-reinforced concrete to withstand more huffing and puffing than one reinforced with plastic. Not so, according to University of New Hampshire civil engineers Robert Steffen and Charles Goodspeed.The two professors have collaborated with engineers in the New Hampshire Department of Transportation on the design and construction of a new bridge in Rollinsford that is the first in the nation to have a concrete deck made with carbon fiber-reinforced polymeric grids buried in the concrete, which was poured earlier this week. The deck has no steel reinforcement whatsoever.
The fiber-reinforced polymer (FRP) has a tensile strength of 160,000 pounds per square inch, notes Steffen, which is over two and one-half times stronger than the yield stress of reinforcing steel. Similar materials have been used in the aerospace industry for some time, in helicopter blades, for example, and on airplane wings.
In situations where salt is present, on New England roads or near the ocean, the steel in conventional concrete is particularly susceptible to corrosion. The concrete deck on the 70-year-old bridge being replaced on Rollins Road had been repaired numerous times.
Steffen has installed more than 80 electronic sensors in the deck and FRP material so that researchers can monitor the bridge's performance for years to come. The FRP grid has performed well in test sections of bridges, but the Rollinsford bridge is the first in theworld to be made entirely with this new grid material. "We can only speculate that there will be fewer deck-patch jobs and thus a longer life span for the bridge," says Steffen. "We hope that this bridge will be a benchmark design in constructing more durable highway bridges in New England and across the country."
Durability is also expected to be enhanced by the use of high performance concrete in the bridge deck and girders. This new concrete mix is strengthened by the addition of silica fume and recyclable waste materials such as fly ash from coal-burning power plants. "The waste materials will not leach out into the environment because the fly ash actually becomes part of the material," says David Gress, UNH professor of civil engineering.
Mark Whittemore, chief of bridge design at the Department of Transportation, worked on the design of the bridge along with DOT engineers Peter Stamnas and David Scott. Whittemore has high hopes for the bridge: "Our intent in working with UNH was to develop a structural system that would outlast our typical approach in the past 20 to 30 years, and come up with a bridge system that will give us a real long life."
Success could benefit both the state and the country. About one-third of the bridges in New Hampshire and across the nation are rated substandard.
Research on the project was funded with a $250,000 grant from the Federal Highway Administration. The bridge will cost $1.4 million, of which 80% is federally funded. Although FRP grids cost five times more than reinforcing steel, notes Steffen, the overall increase in material cost to build the Rollinsford bridge is only 8% higher than the a standard bridge. The increased material cost is offset by reduced labor costs. In addition, it is anticipated that future deck-repair costs will be substantially lower.
Caption: Revolutionary bridge design: Robert Steffen (right), assistant professor of civil engineering, and grad student Jody Trunfio, stand in front of the formwork containing carbon-fiber-reinforced-polymer grids on the deck of a new bridge in Rollinsford on Monday. The bridge, designed by UNH and the N.H. Dept. of Transportation, is the first in the nation to be built with carbon fiber grids, rather than steel, reinforcing the concrete.