The Breaking Point
Civil engineers test safety of box beam bridges
June 1, 2011
About 17 percent of bridges in the state of Ohio are box beam bridges—concrete structures with steel reinforcement embedded inside. They’re commonly used on county roads around Athens, Ohio, says Eric Steinberg, an Ohio University associate professor of civil engineering. Though the Ohio Department of Transportation can visually examine most types of bridges for deterioration, the box beam bridge’s unique construction poses an inspection challenge. That’s becoming a problem, Steinberg says, as many of these bridges are now 50 years old and nearing the end of their projected life spans.
Engineers simulated different types of loads on each of the three spans of this bridge near Washington Courthouse, Ohio, until the structure failed and collapsed. Courtesy of Eric Steinberg
Ohio University and the University of Cincinnati had previously tested individual beams removed from a box beam bridge to gauge durability, but no one had explored how the whole system worked—or failed. The dilemma prompted Steinberg, his team of graduate students and engineers, and colleagues from the University of Cincinnati and the University of Toledo to take the unusual step of demolishing a real bridge in the field.
The engineers found a candidate for their experiment near Washington Courthouse, Ohio. The bridge, which showed evidence of corrosion, featured three spans. After attaching dozens of sensors to the structure and employing ground-penetrating radar, the engineers simulated different types of loads on each of the spans until the bridge failed and collapsed into the creek below it.
Eric Steinberg, photo credit: Kevin Riddell
The data, which engineers continue to analyze, will show transportation officials the types of strengths and weaknesses in box beam bridges and how they hold up to forces such as winter road salt and heavy truck traffic.
“That can help ODOT inspectors decide when to replace these bridges or determine how much of a load can be placed on the bridges,” explains Steinberg, a member of the university’s Ohio Research Institute for Transportation and the Environment (ORITE).
The study findings also could be useful for companies that manufacture and construct the prestressed concrete box beams and other materials used in the bridges’ construction.
By Andrea Gibson
This article appears in the Spring/Summer 2011 issue of Perspectives magazine.