Can Technology Make Bridges Safer?

The U.S. Department of Transportation had declared that “no imminent dangers were observed” on I-35 Bridge in Minneapolis. This was only 13 weeks before the bridge collapsed last August 1. The bridge, built in 1967, was actually rated 4 on a scale of 0 (shut down) to 9 (excellent) devised by the department. Many bridges have similar ratings all over the country, said a department official. The rating essentially means the bridge was safe although there were deficiencies.

It turns out it was not that safe anymore. Many of the country’s bridges are aging, and may need replacement several years from now. When new bridges are eventually constructed, they may carry safety features that are being designed in research laboratories, including high-performance concrete, fiber optic sensors, and robotic snakes.

High-Performance Concrete. A research team from the Iowa State University recently constructed a bridge to test ultra-high performance concrete developed by a French company. The material consists of fine sand, steel fibers, and cement combined in a special way to produce exceptionally strong and dense concrete. Beams that use the material can carry twice the load than standard-concrete beams.

Fiber-Optic Sensors. Researchers at New Mexico State University are testing the possibility of embedding sensors, which would monitor the bridge structure constantly for signs of deterioration. Engineers would then not have to wait two years for bridge inspections to determine the status of the bridge. A fiber-optic cable is hard-wired into the bridge. Light beams would shoot out along the network and sensors at strategic locations would pick up light as it is reflected. The signal is sent to a computer for analysis or, if the stress is too high, for triggering alarms.

Robot Snakes. Bridge inspections are labor-intensive and very expensive. About half of costs is spent for traffic control measures and rigging. Inspectors shut down traffic while one of them hangs on to a basket crane to visually inspect each nut and bolt under the bridge. A research team at Carnegie Mellon University is developing robots shaped like snakes to do the job. One end of the snake has a digital camera to relay video images to a computer. Engineers watch the display while the computer analyzes the data for flaws.

The researchers are also studying how to embed microchips in bridge structures to track various risk factors all throughout their useful lives, from construction to demolition. This would be complemented with laser scanners and other new technology.

Until these useful technologies are deployed in new construction projects, federal and state officials will have to rely on repairs. The Transportation Department has made available federal relief funds for bridge repairs and Congress is authorizing more funds.

A whole lot will be needed. Private civil engineering organizations say the cost to remove bridge deficiencies will run to $9.4 billion annually over a 20-year period. The I-35 in Minnesota in 2005 and the I-70 in Pennsylvania in 2007 bridge incidents should underline the need to give more attention to the country’s bridges.

~ Alain B. Reston for SafetyIssues.com