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Sensor technologies evolving to make highway bridges safer

After the Minnesota tragedy, new inspection techniques may get more scrutiny

By Todd R. Weiss
August 3, 2007 12:00 PM ET

Computerworld - Even as investigators continue to work to recover victims and pinpoint the cause of Wednesday's catastrophic collapse of the Interstate 35W bridge over the Mississippi River in Minneapolis, one topic getting more attention immediately is the availability of systems that can help highway officials better judge the health of the nation's bridges.

Sensor technology to monitor the steel and concrete health of highway bridges already exists and is in use in many areas of the country, while new and improved monitoring systems continue to evolve in myriad research labs and universities.

Vendors, including Physical Acoustics Corp. in Princeton, N.J., and Pure Technologies Ltd. in Calgary, Alberta, already offer intricate portable systems using sensors that can "hear" cracking in bridge cables or steel components so engineers can better assess the conditions of structures.

Meanwhile, engineering research projects, including one at the University of Missouri-Columbia, were already under way long before this week's bridge collapse to advance the science of bridge monitoring. At the school, work is being done on a large-scale sensor system that would be fastened to several concrete bridge piers below a span to alert officials about even the slightest tilting or swaying of critical piers supporting a bridge.

"There's lots of research projects looking at health monitoring for bridges," said Glenn Washer, an assistant professor of civil engineering at the school and an expert in the field. "There are some technologies right now that are in use monitoring bridges."

Minnesota Department of Transportation officials could not be reached this morning to determine if any such systems were in use on the collapsed bridge or on any other spans in the state.

Washer said that existing monitoring systems from Physical Acoustics and Pure Technologies collect "acoustic emissions" given off by fracturing metal. "If a piece of steel is under force and it fractures, it gives off a tremendous amount of energy" in the form of sound waves that can be detected and interpreted by a sensor system. It's not uncommon for some of the individual steel strands that make up bridge cables to break over time, he said. Officials can use the sound-sensing systems to track how many of the thousands of strands in a cable are damaged before maintenance is required.

What makes the research done by Washer's team different is the focus on monitoring bridge supports for problems. A prototype is expected to be ready for testing and in the field in about six months, he said. "I think there will be more of a focus on these kinds of technologies and more investment" in light of the Minneapolis bridge collapse.

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