Cincinnati -- If Charlie Brown had set out to buy a bridge instead of a Christmas tree, he probably would have picked out the little bridge over Seymour Avenue in nothern Cincinnati. There it sits ... rusting ... crumbling ... abandoned for years.
But the unremarkable little bridge in northern Cincinnati has begun to attract the attention of scientists and engineers worldwide. That's because the bridge is now a national test site for researchers looking for better ways to monitor the health of the nation's highways.
"Why is this important? We have half a million bridges in the country, and all the information we have on these bridges is based on visual inspections," explained Ahmet Aktan, professor of civil engineering and director of the Cincinnati Infrastructure Institute at the University of Cincinnati.
The bridge used to connect a church with a local mental hospital. It was abandoned when the surrounding land was sold. Although its condition has deteriorated, the bridge proved to be an ideal test site because its design is similar to tens of thousands of other bridges still in use.
Aktan is leading the studies on the bridge in collaboration with electrical engineering associate professor Arthur Helmicki and mechanical engineering professor David Brown. However, the collaboration has spread far beyond UC.
"We are working with an international panel," said Aktan. "We have Los Alamos National Laboratories, the U.S. Air Force, Texas A&M, a federal lab in Switzerland and Imperial College in London, among others."
The widespread collaboration means that Aktan can use technology that isn't available anywhere else. For example, one piece of equipment used to send vibrations through the bridge was originally designed for use by the military. Federal funding for defense conversion projects made the equipment available for the bridge testing project.
A typical experiment involves "exciting" or vibrating the bridge to mimic the loads from heavy traffic. This tells the researchers how well the bridge holds up under stress. However, long-term monitoring of the bridge turned up another interesting finder. Aktan said daily temperature changes can be just as devastating as a heavily loaded truck.
"Early in the morning, if you're coming from a cold evening, the bridge is one bridge. But as the temperatures get higher at 10 a.m., the bridge has turned into a different structure.
"The impact was beyond our comprehension. It is affected by humidity. It is affected by temperature. It is affected by the overall average seasonal temperature, and nobody had any hard data on how much a large civil structure like this would be affected by environmental conditions."
The UC researchers are using two different types of sensing systems to monitor changes in the bridge. In addition, they're using a unique photogrammetric camera system which can detect even the most minute shifts or slips. Jay Yocis, a graduate student from the College of Design, Architecture, Art and Planning, is exploring photogrammetry as a research tool.
"This is a very special photograph that permits you to develop a computer image of the bridge with dimensions accurate to about 1/16 of an inch," according to Aktan, who says that accuracy matches the accuracy of the most sensitive laser-based systems on the market today. Photogrammetry is also faster and less expensive than traditional surveying.
The system has another clear advantage. It is portable. Long- term bridge monitoring by other methods require a small trailer full of equipment.
Aktan will present his preliminary findings on the bridge project to the National Science Foundation and the Federal Highway Administration this fall and a more detailed report at the International Modal Analysis Conference in Orlando this winter.
The project is funded by both federal agencies with additional support from industry, the Ohio Department of Transportation and the Ohio Board of Regents.