In 2009, the American Society of Civil Engineers gave the overall U.S. infrastructure a "D" in a report and claimed that all levels of government should invest $2.2 trillion over five years to improve - the nation's bridges alone earned a "C."
Research now in progress may help bring those grades up. "A significant amount of research and product development is under way to advance the capabilities and usability of bridge inspection and monitoring technology," said Ian Friedland, technical director of Bridge and Structures Research and Development in the Federal Highway Administration's Office of Infrastructure Research and Development. "In addition to work sponsored by the Federal Highway Administration, other federal and state agencies are supporting these efforts, along with industry and academia."
Sometimes it takes a disaster, like 2007's Interstate 35W bridge collapse in Minnesota, to spur action. Today engineers at the University of Minnesota (U of M) use hundreds of sensors on the replacement bridge to analyze data and develop 3-D models of the information.
"We have 500 sensors throughout this structure that's 1,200 feet long, down into the piers and foundation as well," said Catherine French, a civil engineering professor at U of M who leads the project. "A lot of effort has been put in by the university to do the data interpretation and also develop a system that can be used for long-term monitoring of the bridge."
French and her colleagues intend for the data to help them see how damage and fatigue could occur from various factors, including temperature and load pressure.
"Certain design assumptions and modeling tools are used in designing bridges," French said. "This gives us an assessment of whether the assumptions made in the design of the bridge were accurate."
The story is similar with the Tacony-Palmyra Bridge in Philadelphia, which is managed by the Burlington County Bridge Commission. The commission let Drexel University use the structure for experimental analysis that could affect the future of structural health monitoring.
"The project will leverage different modalities of sensing and imaging: point sensing, distributed sensing based on electronic, optical or acoustic sensors; video imaging; infrared imaging; etc.," said A. Emin Aktan, a professor of infrastructure studies at Drexel and director of the university's Intelligent Infrastructure and Transportation Safety Institute.
The project began in fall 2009, and Drexel plans for classrooms to receive live sensor and video clips from the bridge for assignments. "We should be able to push the button on the computer and project the bridge onto the screen for all students to see," Aktan said. "We should be able to see the cars and trucks moving. We should be able to look at the weather."
Dave Lowdermilk is a vice president at Pennoni Associates, the firm that's the commission's resident engineer and a partner in the project. He said research on monitoring the structural health of bridges and other transportation infrastructure often is impeded by tight federal funding. "We're fortunate that the Burlington County Bridge Commission is a self-sustaining organization through toll collections. They [can] do a lot of the work that they need to through toll revenues," he said. "State [transportation departments] and other agencies that rely on federal dollars are at a loss right now."
The federal government authorized the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users to fund highway research programs from 2006 to 2009. Congress extended it through December 2010. In January 2009, the National Institute of Standards and Technology announced about $88 million in awards for research to develop sensors to aid in structural health monitoring projects over the next five years.