Best Bridge Inspections Involve More Than Meets the Eye, Say Experts

August 6, 2007

The main protection against collapsing bridges in America are the eyes and ears of inspectors like Jody Ferris, who on Friday was checking a repaired weld on a 34-year-old bridge with some pretty low-tech tools: flashlight, hammer, ruler and camera.

Experience is what counts, said Ferris’ boss, Joe Miller of the Maryland Department or Transportation. “Nothing is better than the human element.”

Many in the industry disagree, and a federal test of bridge inspectors gives them reason for concern. On one bridge, a fifth of the inspectors missed serious problems.

“Visual inspection is just not enough to be absolutely certain you have no cracks,” said Steven Fenves, a researcher at the National Institute of Standards and Technology. “A guy has a little hammer in his hand, he knocks down a few flakes of rust and a few flakes of paint and tries to make sense of it while fearing for his life in a dangerous situation.”

Fenves said inspection methods could be improved, especially by using better technology: “Much of it involves bridge inspection by a very tired bridge inspector who has just climbed up a bridge and is dodging pigeons…. It’s a very inadequate process.”

A 2001 federal highway research study that put 49 inspectors from 25 states to real-life tests found that their training, experience and ability to spot cracks and see other defects in bridges was spotty at best. Many are well-trained, but others flunked the test.

One test involved an in-depth inspection of the key supporting steel of a test bridge on Route 1 in Northern Virginia. “The overall accuracy rate for correctly identifying” tiny cracks that were just starting to form was less than 4 percent, the report said. When it came to weaknesses in bolt connections, the accuracy rate was 24 percent.

On a second Virginia bridge, one-fifth of the inspectors missed what testers called “severe deficiencies.”

The inspectors were graded on a scale of 1-10 for thoroughness with 10 being the highest. Overall, 45 percent got grades of 8 or higher. However, 36 percent got ratings of 0 to 4 with the report saying they delivered “an incomplete in-depth inspection.”

The testing was done by researchers at the Federal Highway Administration’s evaluation center in McLean, Va.

The methods and knowledge of bridge inspectors — who are hired by states but must meet minimum federal standards — varies greatly, said University of Missouri civil engineering professor Glenn Washer. He co-wrote the study when he was a research engineer for the highway administration.

Washer says he “isn’t so worried about the quality of people doing the inspecting,” but the effectiveness of the different methods used.

In 2005, the federal government required states to adopt new quality-assurance processes for testing, but it’s too early to tell how those are working, Washer said. Also, some states outsource their bridge inspections to private firms, experts say. There are minimum standards for training, and some states, like Maryland, go farther.

Still, it’s the visual inspection process itself that needs upgrading, other experts said.

Inspectors at times can’t even see everywhere they need to see. That’s especially true of bridges built before the 1967 collapse of the Silver Bridge over the Ohio River — an event that forever changed design rules, said Fenves and James Garrett, an infrastructure expert at Carnegie Mellon University.

Garrett and others have developed high-tech constant monitoring systems for bridges. Garrett’s is aimed to be constructed into the guts of new bridges. A handful of companies are looking at retrofit systems that could be attached to the nearly 600,000 bridges in the United States, where one in four are considered deficient in some way.

Peter Vanderzee of LifeSpan Technologies in Atlanta has a bridge retrofit system with 24-hour sensors. For large bridges, like the one in Minneapolis that collapsed Wednesday, it would cost $250,000 for comprehensive sensing for cracks and strain.

But state highway departments usually say no to Vanderzee and his competitors. The reason: lack of money.

Another reason is newness. Richard Sause of Lehigh University said he isn’t sure new high-tech monitoring systems are developed enough to be reliable.

“They’ve been proven,” Vanderzee counters. “They’re used more in Asia and Europe than they are in the United States. Go figure.”

Until then, it’s up to Ferris inspecting welds up in a cherry-picker more than 20 feet off the ground just under Interstate 70. He scraped away bird droppings to have a better look at the weld, and then he struck it with a hammer.

For both steel and the concrete abutments nearby, sound is key, said bridge inspection chief Miller. Good concrete makes a “ping” sound, and bad concrete makes a thud, he said.

On Friday, Ferris hears only good sounds and finds the bridge in good shape. He said he knows how important his role is in bridge safety: “We take our job seriously.”


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The 2001 Federal Highway Administration study on bridge inspectors:

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