Technology could bridge safety gap

Civil engineer Tripp Shenton likens current bridge inspection practices to “a doctor working without a stethoscope, without X-rays or EKGs.”

The collapse of an interstate highway bridge in Minneapolis -- and the frightening images of cars plunging into a river -- may force a high-tech update.

Most bridge inspections now are conducted just as they were decades ago, with binoculars to scour for cracks and a hammer to knock against trusses to test for hollow spots.

The 21st century version?

Imagine a web of sensors capable of measuring hairline cracks in steel -- and sending out an alarm when one of those cracks begins to widen. Another network might continuously check stress loads on the bridge, recording the data on a seismograph that would spike at the first sign of trouble.

“You could set it up so the bridge can call you if something abnormal occurs,” said James A. Swanson, an engineering professor at the University of Cincinnati.

This technology is being used on bridges in a few states, including Pennsylvania, Ohio and Utah. Other diagnostic tools are also under development -- often with federal grants -- in engineering labs from coast to coast.

“There are people everywhere working on this,” said Shenton, associate professor of engineering at the University of Delaware.

Mississippi State University professor Charles A. Waggoner rigged his inspection device from an unlikely assortment of household items: a jogging stroller, a lampshade, a microphone and a laptop computer.

The contraption drags metal chains across a bridge deck and analyzes the sound vibrations, mapping the pings and clunks into a grid that indicates which sections are corroding from within.

That’s not even the most offbeat device.

At New Mexico’s Los Alamos National Laboratory, engineer Chuck Farrar developed sensors that can tell when a bolt is coming loose or a weld is weakening. But how are the sensors powered? With a remote-controlled model helicopter, of course. The toy chopper hovers over the bridge, shoots microwave beams to activate the sensors and then records the data to an onboard computer.

If all this sounds a bit far out, it’s supposed to. Promoters say it’s long past time to leap into a new era of bridge inspection.

Their best sales pitch: A 2001 federal study that put traditional hammer-and-binoculars inspections to the test.

For that study, the Federal Highway Administration convened 49 inspectors from 25 states and asked them to examine bridges that had been thoroughly examined for defects. The inspectors identified only 4% of emerging cracks and 24% of suspect bolts.

The results also showed how subjective visual inspection could be. One team rated the superstructure of a test bridge at four on a zero-to-nine scale, indicating poor condition. Another team rated the same aspect of the bridge at eight, deeming it near-perfect. (The federal government gave it a five.) Wide variations also showed up in the ratings for other bridges.

The federal test drew scant attention when it was released. Now, however, it’s being reviewed against the backdrop of daily updates from Minneapolis, where recovery workers are still struggling to pull victims and crushed vehicles from the wreckage.

Transportation Secretary Mary E. Peters has ordered the department’s inspector general to conduct a “top-to-bottom review of the bridge inspection program”; the report should be completed within the year.

Nearly 75,000 bridges nationwide -- including about 2,800 in California -- are rated “structurally deficient,” as was the Interstate 35W span in Minneapolis that tumbled into the Mississippi River. Another 80,000 are considered “functionally obsolete,” meaning they are not up to handling the demands of modern traffic. Many states still use bridges built in the 1920s, ‘30s and ‘40s. (The failed bridge in Minnesota opened in 1967.)

Federal law requires that bridges be visually inspected every other year. But the amount of funding states dedicate to such exams varies wildly.

Minnesota spent $2.3 million last year on bridge inspections. California -- with 76 inspectors -- spent $15 million.

“Every state right now is reviewing their inspection program,” said Malcolm T. Kerley, chief engineer for Virginia’s Department of Transportation. Virginia spent $13.5 million on inspections last year. “If we think we need to put more money in there, we will.”

The intense interest in bridge inspection has been boon and bane to vendors of new diagnostic devices.

Robert M. Bernstein, CEO of Material Technologies Inc., says that since the evening the Minneapolis bridge collapsed, he’s been bombarded with so many inquiries, he hasn’t even had time to read his e-mail.

“There’s got to be 200 messages piled up,” he said. He was on TV twice -- once on NBC and once on Fox. “My chief engineer has been on three times. It’s been a real nightmare,” he said.

But a potentially lucrative one: the Los Angeles-based company sells sensors that use an electrolyte gel to detect whether minute cracks in steel girders are holding steady or expanding.

“There’s no question in my mind,” Bernstein said, “that this will be very, very significant for the growth of our company.”

The holdup, as always, is cost.

Peter Vanderzee, chief executive of LifeSpan Technologies -- which sells sensors that measure stress and cracking -- said he could wire a bridge as large as Minnesota’s I-35W for $250,000. Swanson estimates that the fully automated, page-us-when-something’s-wrong system he developed at the University of Cincinnati might cost $500,000 for a bridge that size.

Those systems only measure stress on the bridge.

It could cost tens of thousands more to automate underwater inspection with fiber-optic probes embedded next to pilings. (The probes, under development at Alabama A&M; University, monitor erosion around a bridge’s underwater supports.) Identifying pockets of unstable land around the bridge with a satellite map produced by the German firm Goeka could cost up to $10,000.

Given those price tags, the latest innovations will likely be used on just the most visible -- or most vulnerable -- of the nation’s 600,000 bridges, said Kelley C. Rehm, a bridge engineering expert with the American Assn. of State Highway and Transportation Officials.

“I don’t think states will be testing some crazy new technology on their run-of-the-mill bridges,” Rehm said.

Even where computerized sensors are deployed, engineers caution that no system can ever analyze every possible point of failure on a large bridge like Minnesota’s I-35W.

“You could use every one of these technologies and they may or may not alert you as to what’s happening on that bridge,” Shenton said.

If an alert does come in, visual inspectors -- armed with old-fashioned tools -- will likely be sent out to verify the problem and figure out what to do.

One common response is restricting weight load by barring heavy trucks, but such postings are often ignored. “Unless you have a state patrol sitting there, you can’t stop them from going across. That’s a real worry, because theoretically the bridge is not strong enough to carry them . . . and at any moment, a stringer could snap,” said Jeff Anderson, manager of Colorado’s bridge inspection program.

“There’s more to it than just putting technology on bridges,” Kerley said. “It’s not just about collecting data. The question is what you’re going to do with it.”

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stephanie.simon@latimes.com