CORVALLIS - Space age technology and Oregon State University engineers have provided a new lease on life for the historic Horsetail Creek Bridge in the Columbia River gorge. And the innovations used to save this 85-year-old relic may soon help rescue decaying infrastructure across Oregon and the United States.
For civil engineers who were weaned on concrete and steel, the new "fiber reinforced polymers" now carrying traffic over Horsetail Creek are nothing short of a revolution, OSU researchers say. And they hold the potential to address a growing, $200 billion national crisis.
"There's a huge need to repair existing structures such as historic buildings and bridges, which are deteriorating faster than our ability to replace them ," said Damian Kachlakev, an assistant professor of civil engineering at OSU. "It's a really scary and very costly problem."
There's also a need, he said, to develop more economical systems for the future of the construction industry. These fiber reinforced polymers, or FRPs, have had aerospace and military uses for years. But the mainstream construction industry is just now waking up to their potential to solve some chronic problems in retrofitting existing structures and economically building new ones.
Five times lighter than steel, up to 10 times stronger and with a corrosion resistance that should make them last longer than any conventional material, the FRPs resemble cloth and are made from such composites as fiberglass, carbon and aramid, combined with special types of epoxy or vinyl resins. When applied, they create a flexible but incredibly strong material about the thickness of a sheet of plastic laminate.
"When you see FRPs being applied, it looks more like a pharmacy than a construction site," Kachlakev said. "And the actual process is more like hanging wallpaper than laying a reinforced concrete beam."
In the case of the Horsetail Creek Bridge, the Oregon Department of Transportation was facing an Oct. 1, 1998, deadline to either upgrade the strength of the historic structure or close it to traffic. Reinforcing steel had probably corroded in the bridge and it had an inadequate structural design in the first place, Kachlakev said. It was 96 percent deficient in shear strength and unsafe by current standards.
But by taking advantage of OSU's developing expertise in testing, evaluating and working with the new FRP materials, ODOT opted to save the attractive structure that spans Horsetail Creek. Workers from ConTech Services, Inc., of Vancouver, Wash., did the actual application of the FRP reinforcement.
With this technology, cloth-like sheets of material are impregnated with resins and then carefully applied to the surface of weakened concrete supporting beams on the original structure, taking maximum advantage of the fiber orientations of the new product.
When completed, the materials were coated with a finish resembling the original concrete of the historic bridge, and implanted with fiber optic sensors that will help scientists monitor the FRP performance over time and under various loads.
So while the bridge continues to quietly serve as a charming reminder of Oregon's transportation past, it will also be playing a vital role in perfecting technologies for the future, Kachlakev said.
"ODOT estimates that about 75 percent of the bridges in Oregon need strengthening," Kachlakev said. "That's just a fraction of the problem we face nationally and internationally on bridges and other structures, at huge public expense. We think FRP materials can play a major role in solving this crisis."
Interest in using these materials in construction is increasing rapidly, he said. This has prompted OSU to begin new research programs that will test various types of FRPs and help develop national building standards for this technology, while making OSU civil engineering faculty and graduating students among the most highly trained in the nation in use of these systems.
Kachlakev and College of Engineering colleagues Thomas Miller and Solomon Yim already have seven graduate students using study of these materials for their advanced degrees. In just the past year the blossoming OSU research program in this area has attracted more than $300,000 in grants and FRP industry support, and a steady interest promises more research funding in the near future, he said.
Among other initiatives, near-exact replicas of the massive concrete beams that support the Horsetail Creek Bridge have been built and are being studied in OSU laboratories. OSU scientists are not only studying existing FRP systems in Europe, Japan and the U.S., but are developing their own.
And more good news - FRP materials are comparatively cheap.
"Just the cost of enlarging a couple of existing concrete beams to support the Horsetail Creek Bridge would have been $70,000, not counting all the other hidden expenses and public inconvenience for closed traffic during construction," Kachlakev said. "With this technology, we were able to repair the whole structure for a total of $30,000. It looks almost identical to the original and the bridge didn't even need to be closed while the work was going on."
Although considerable research remains to be done to encourage more widespread use of this technology, Kachlakev said it's already clear that it will be playing a major role in the future of the United States - and global - construction industry. The materials are strong; relatively inexpensive due to minimum labor and equipment requirements; resist corrosion and earthquakes; and easy to apply.
And the Horsetail Creek Bridge - the first bridge in the United States to ever use these new materials to correct such a severe structural deficiency - may quietly serve its graceful role in the Columbia River gorge for another century or two.