By Kevin Wilcox
A remote and deteriorating West Virginia span has been returned to its design capacity after FRP wrap and concrete were used to bolster rusted steel bents.
The concrete and fiber-reinforced polymer not only strengthened the bridge but also arrested corrosion. Courtesy of Hota GangaRao
May 9, 2017—East Lynn Lake, in scenic Wayne County, West Virginia, is a popular destination for outdoor enthusiasts, drawn by the reservoir's many species of stocked fish as well as boating and camping opportunities. The reservoir is part of a flood control project completed in 1970 and is operated by the U.S. Army Corps of Engineers district headquartered in Huntington, West Virginia.
The only route to the lake crosses a 126 ft long concrete bridge founded on steel bents, and over the decades, those steel H-pile bents have corroded significantly. In 2013, roughly 44 years after the bridge was completed, the Corps reduced the span's capacity from 15 tons to 6 and limited traffic to a single lane.
Replacing the bridge would have been complex and expensive. It would also have required discarding a reinforced-concrete deck that was still in good condition. Instead, a team of researchers from West Virginia University (WVU), working with the Corps in an initiative sponsored by the National Science Foundation called the Center for the Integration of Composites into Infrastructure, successfully rehabilitated the bridge and in the process validated a process for renewing the rusted steel bents with fiber-reinforced polymer (FRP) jackets.
The FRP composite used in the project begins with a flexible sheet of glass fiber that is bonded with a polymer resin. The resulting material is exceptionally strong and airtight, two qualities needed for the East Lynn Lake bridge.
The team was led by Hota GangaRao, Ph.D., P.E., F.SEI, F.ASCE, the Maurice A. and Joann Wadsworth Distinguished Professor of Civil and Environmental Engineering in WVU's Benjamin M. Statler College of Engineering and Mineral Resources. GangaRao directs the school's composites center and has been experimenting with FRP for decades, but this was the first time he had used it to rehabilitate rusted steel structural members.
Before the project, the bridge’s steel bents were badly corroded, forcing a weight limit reduction. Courtesy of Hota GangaRao
"The challenge was how [we were] going to use this kind of material without disturbing the basic configuration of the steel bridge structure," GangaRao recalls. "The steel wide-flange columns were badly corroded. How do I transfer the forces from the bridge deck to the columns [and] from the columns on down to the foundation? That was a challenge. Then how do I wrap this inconvenient cross section?"
So he contacted material suppliers and selected a fiber jacket manufactured by Simpson Strong-Tie Company, Inc., of Pleasanton, California, that could encase a column as a continuous unit, as well as a fiber wrap from Air Logistics Corporation, of Monrovia, California, that could be installed around that jacket.
Early exploratory work found that the steel bents were well preserved just 2 ft below the mud line. The team used a power washer to remove rust scales from the bents, treated them with a rust inhibitor, and determined the best locations for welding steel studs. These studs would help transfer loads to the concrete that was to be poured around the bent.
Once the round jacket was slipped around the bents and "zipped up," GangaRao explains, the team placed a special epoxy concrete into it up to a point above the waterline and then filled the rest with conventional concrete. Once that was complete, two more layers of FRP were wrapped around the fiber jacket.
"This provides a huge amount of reserve strength to each and every one of those columns," GangaRao says. "In addition, concrete and the FRP jacket hermetically sealed the corroded columns; therefore, there is no oxygen content going in there. We put some corrosion sensors in that bridge, and we are not finding any kind of additional corrosion-related activities progressing. It is completely arrested."
The team conducted static and dynamic load tests of the bridge both before and after the rehabilitation. Those tests revealed that the load-carrying capacity was 10 times higher under static loads and 6 times higher under dynamic loads after the project, GangaRao says. This enabled the Corps to return the bridge to its original weight limit.
"We expected it to perform that well," GangaRao says, adding that knowing it on paper and demonstrating it in the field are different experiences. "You always feel good when it performs the way you expect it to perform based on computational analysis."
The bridge is now outfitted with a series of strain gauges, temperature monitors, and corrosion sensors. A team under the supervision of Udaya B. Halabe, Ph.D., P.E., F.SEI, F.ASCE, a professor of civil engineering at WVU, continues to monitor the performance. Mark Skidmore, P.E., M.ASCE, an engineering scientist at WVU who participated in the rehabilitation, is responsible for this ongoing effort. The data coming back from the sensors indicate that the rehabilitation is working as planned.
As an added benefit, the project took just three weeks to complete, compared with perhaps more than a year for a full replacement.
GangaRao is investigating the longevity of FRP materials in the field, which is an open question for the relatively new material. He is also exploring how the material might be modularized so that it could be delivered to jobsites with the resin and polymer already bonded, which would minimize inconsistencies in on-site application methods.
"FRP renewal is not a panacea, but [when] it can be done—especially coupled with conventional construction materials—it saves huge sums of money," he says. "Europeans do a much better job of preserving their infrastructure than we do. Somehow, we have a culture of get rid of it and replace it with a new one.
"We spent about 20 to 25 percent of the replacement cost for rehabilitating this bridge," he says. "My message is simple—do not rip and replace, but renew with FRP where possible."