Professor speaks about Washington bridge collapse

May 29, 2013
Dr. Keith Thompson

PLATTEVILLE, Wis.­­­ — University of Wisconsin-Platteville professor Dr. Keith Thompson gives insight into rising concerns of aging infrastructure after the Washington state I-5 bridge collapse May 23.

“I am not surprised by this bridge collapse,” said Thompson. “Bridge problems happen all the time unfortunately. This particular bridge was classified particularly as functionally obsolete, meaning the bridge could be too narrow for what they consider for convenient traffic limits, or that they don’t have enough clearance over the bridge. If the clearance is not high enough, trucks can clip it, which is what happened in this case.”

Thompson is a structural engineer and associate professor in the UW-Platteville Department of Civil and Environmental Engineering and teaches Introduction to Infrastructure, Structural Mechanics and Reinforced Concrete.

He stated that the I-5 Mount Vernon, Wash., bridge also fell into another category called fracture critical, meaning if one part of the bridge were to become too damaged, it can lead to a collapse of the entire bridge. “This fracture critical classification is common among older bridges,” he said.

According to the American Society of Civil Engineers, there are 607,380 bridges in the United States, each bridge averaging about 42 years old.

“Even though this bridge was reportedly inspected twice last year, the problem is not with the bridge inspection standards. The problem is the number of bridges,” said Thompson. “It is simply too expensive and requires too much person power to maintain all of these bridges. We have aging infrastructure that is beyond our capacity to keep up with.”

This particular bridge was reportedly built in 1955, and has approximately 71,000 vehicles using that stretch of interstate everyday.

“Most bridges don’t collapse because of weight or traffic on top of them. Damage to the supports from flooding underneath is the most common cause of failure. Age-related corrosion is another concern. Statistically, trucks have gotten bigger and heavier, but bridges are typically strong enough to hold them. There is a very large factor of safety that goes into the design and building process,” he said.

Thompson also explained the failure rate of bridges is relatively small in all of the bridges in the United States. “But if by chance, one truck attempts to cross a bridge that was not satisfying the clearance limits on the bridge, and it manages to clip the overhead infrastructure on the bridge, you then have an accident on your hands that is just bound to happen,” he said.

Contact: Dr. Keith Thompson, associate professor, civil and environmental engineering, (608) 342-1479,

Written by: Eileen McGuine, UW-Platteville University Information and Communications, (608) 342-1194,


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