Engineering safer bridges
The partial collapse of a New York state bridge a couple of years ago may prove to be a milestone of sorts in the maintenance of America’s civil infrastructure.
Dunn Memorial Bridge, which spans the Hudson River in New York to connect Albany and Rensselaer, was temporarily closed in July 2005 when a portion of one of its access ramps slipped off its bearings and fell several inches. Subsequent investigation determined that the bridge buckled because its concrete support piers had tilted and cracked.
Research sparked by the New York bridge accident and now under way at the University of Missouri–Columbia aims to prevent future collapses. Glenn Washer, an MU civil and environmental engineering assistant professor, started work after hearing of the New York accident on an interactive sensor system that would continuously monitor bridge piers and warn of incipient weaknesses.
“We’re trying to develop a system that will provide a cost–effective monitoring tool to increase the reliability and safety of the highway system,” Washer said.
Washer recently received a $109,500 grant from the National Academy of Sciences to develop the integrated system, which he expects to complete by the end of this year. While sensors already help assess the condition of a few bridges, Washer’s sensor network would allow government inspectors to replace short–term, on–site sensor analyses and testing with long–term continuous remote monitoring.
Washer said his network of about 20 sensors also would provide far more sensitive information and last longer than current sensor systems, which generally do not share information and lose their effectiveness in a couple of years.
“The instrument we’re going to develop is intended to monitor tilt over long periods of time, between 10 and 20 years,” he said.
It’s an instrument that might well prove useful throughout the country.
Nearly 14 percent of the nation’s bridges were classified as “structurally deficient”—that is, deteriorating—as of 2004, according to the latest report issued by the Federal Highway Administration (FHWA). That doesn’t include those bridges deemed “functionally obsolete” in 2004, which account for another 13–plus percent that may be structurally sound but no longer meet transportation standards and demands.
Closer to home, 31 percent of Missouri’s bridges are either structurally deficient or functionally obsolete, according to a Better Roads inventory published in November 2006. The magazine is geared towards the governmental highway and bridge construction industry.
A leading federal highway official points to the reliable information and specific measurements that Washer’s sensor system would provide those working to maintain the national infrastructure.
“Research and development of technology to assess the condition of highway structures and measure their performance is an essential element of our national strategy to collect the information necessary to effectively manage civil infrastructure throughout its life cycle,” said Steven B. Chase, chief scientist at the FHWA’s Turner–Fairbank Highway Research Center in McLean, Va.
Fittingly, the New York State Department of Transportation will test Washer’s sensor network prototype.
New York’s DOT, which is pitching in $12,000 to cover the prototype’s installation cost, will evaluate the system on an upstate New York bridge at the end of next year. The trial run will last six months.
If successful, the system could provide a relatively inexpensive way to help keep the nation’s bridges safer.