Wisconsin to start experiment with bridge-failure sensors

  • Article by: Mike Kaszuba and Jake Sherman
  • Star Tribune staff writers
  • September 27, 2007 - 9:57 PM

In the days following the Interstate 35W bridge collapse, Wisconsin Gov. Jim Doyle ordered that 14 bridges of similar design in his state be fitted with special sensors, known as strain gauges, that can detect unusual movement. Installation will begin in October.

In Minnesota, Gov. Tim Pawlenty instead opted for stepped-up inspections of potentially vulnerable bridges, and the Minnesota Department of Transportation has continued a policy of using strain gauges only on research projects.

The different responses reflect the continuing debate over the role of high-tech devices in detecting potentially fatal problems in bridges. Inspections are still carried out by workers peering into the bridge's many crevices, and even the strain gauges to be used in Wisconsin rely on technology that is two decades old.

Newer devices, such as an electrochemical sensor to detect metal fatigue, are considered experimental, even by states that are using them.

"It's still kind of an emerging technology, so a lot of it is being done by researchers at universities," said Prof. Harry (Tripp) Shenton of the University of Delaware's Center for Innovative Bridge Engineering. "There aren't a lot of companies that specialize in it."

Almost immediately after the bridge collapse, U.S. Rep. Jim Oberstar, D-Minn., criticized MnDOT on the House floor for having passed up a chance to install on the I-35W bridge newly developed technology offered by Material Technologies Inc.

"I am disappointed that the state rejected the opportunity," he said.

The California company's chief executive, Robert Bernstein, claims the company's electrochemical fatigue sensors could have detected growing cracks in the bridge. "If that was their objective -- to find fatigue-critical locations and growing cracks and examine them appropriately -- yes, our technology would've found them," Bernstein said.

He explained that the sensors work similarly to an electrocardiogram: They are placed throughout the bridge and as cars rumble over the span, they are able to detect small cracks.

In Washington, Oberstar and former Pennsylvania Rep. Bud Shuster, who now works for Material Technologies as a lobbyist, touted the technology. Shuster recommended the company to Oberstar.

"Yeah, I called his staff, spoke to Jim about it," Shuster said.

Minnesota's concerns

MnDOT spokesman Kevin Gutknecht said the agency was aware that Material Technologies tried to persuade URS, a MnDOT consultant on the I-35W bridge, to use the sensors.

"First, it doesn't have a long track record yet and, second, some of the pieces and some of the issues with the installation would make it very cumbersome and difficult to use," Gutknecht said. "What we've done with it is we're keeping track of it, and we may have some structures it may be good for in the future."

Finn Hubbard, Wisconsin's state bridge engineer, said he is not yet convinced of the technology.

"[It's] still, in my opinion, a little bit futuristic," he said. Hubbard also said the company's sensors have to be placed over a crack -- meaning one has to know there already is a crack there -- to measure whether it is expanding.

"Fatigue sensors [are] very, very new," he said. "I would definitely agree with [MnDOT] that it's somewhat experimental."

A Federal Highway Administration spokesman said the agency has purchased the technology from Material Technologies to test it for widespread use. Five states -- Pennsylvania, Massachusetts, New York, New Jersey and Utah -- also have contracts with Material Technologies, the company said.

The Pennsylvania Department of Transportation uses Material Technologies' EFS technology as one of its bridge-inspection tools, said Rich Kirkpatrick, a spokesman for the department.

He declined to say whether the state was satisfied with the equipment.

None of the bridges where the technology is being used in Pennsylvania is as large as the I-35W bridge or carries its high volume of traffic, he added.

3-month Wisconsin test

In Massachusetts, state transportation officials are using Material Technologies as part of a pilot program. "It's still early in the process for us," said Erik Abell, a department spokesman. "We're still reviewing some of their findings in their first round of work."

The strain gauges that Wisconsin will be installing beginning next month will be used to collect measurements for about three months.

The bridges include two that reach Minnesota: The Hwy. 243 bridge over the St. Croix River at Osceola and the Hwy. 14-Hwy. 61-Hwy. 16 bridge over the Mississippi River near La Crosse. Wisconsin is contracting with three companies for the sensors, at a cost of about $300,000, Hubbard said.

"It's all about getting the information as quickly as you can," he said.

The definition of "quickly" is changing, however. When the program was announced in August, the sensors were to have transmitted data as it was collected to WisDOT headquarters. But on Sept. 17, Chris Klein, the department's executive assistant, said the sensors would not report data in real time after all.

Mike Kaszuba • 612-673-4388 • Jake Sherman • 202 408-2723 •

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