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Bridge Inspections Under Scrutiny After Minneapolis Collapse

August 13, 2007 at 6:10 PM EST
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JIM LEHRER: Navy divers continued searching for missing victims of the bridge collapse in Minneapolis today, while inspectors checked the condition of many bridges around the country. More than 73,000 bridges are rated “structurally deficient” by the U.S. Department of Transportation. NewsHour correspondent Betty Ann Bowser has our Science Unit report on what inspectors are looking for.

BETTY ANN BOWSER, NewsHour Correspondent: As one of the 18 full-time bridge inspectors in Missouri, Kevin Wegener spent most of the past week suspended in mid-air over the side of a steel-truss deck bridge, almost identical to the one that collapsed in Minneapolis.

The Hurricane Deck Bridge is a 72-year-old structure over the Lake of the Ozarks in southwestern Missouri. For Wegener, it’s not just business as usual. As he visually surveys the condition of the bridge, Minneapolis is ever present in the back of his mind.

KEVIN WEGENER, Bridge Inspector: I watched the whole thing. And it kind of makes you think, like, say when you go down to make sure you look at everything thorough and don’t miss nothing and…

BETTY ANN BOWSER: He looks carefully at the pieces of steel held together at their joints with gusset plates, the framework that makes this a truss bridge. He wants to know if there are any signs of rust, corrosion or cracks. In addition to looking below the bridge, he also carefully surveys the top, known as the bridge’s deck.

What are you trying to capture in these photographs right now?

KEVIN WEGENER: The full length of the driving surface, joints, hand railing, curbing.

BETTY ANN BOWSER: And what are you looking for?

KEVIN WEGENER: Deficiencies.

BETTY ANN BOWSER: And he finds a couple: first, a crack in the pavement; then, something potentially more serious.

KEVIN WEGENER: The joint has a tear, about a two-foot tear. It’s actually letting water go through.

BETTY ANN BOWSER: Is that bad?

KEVIN WEGENER: It can be. The joint is actually where your expansion device is at that lets it expand and contract. If a bridge don’t move, that’s not good. It should have movement.

Fixing Missouri's bridges

BETTY ANN BOWSER: Two years ago when Wegener inspected it, Hurricane Deck was rated a six on a scale one to nine, one being the worst. Then it was deemed safe. Now Wegener says he doesn't see much change. He reached his conclusion almost exclusively on what he saw. In this high-tech age, bridge inspection is still highly dependent on the human eye.

INSPECTOR: Any changes?

CARL CALLAHAN, State Bridge Maintenance Engineer: Haven't heard anything yet.

BETTY ANN BOWSER: Missouri's top bridge inspector and Kevin Wegener's boss, Carl Callahan, thinks his crews do a great job, but he does have one big worry.

CARL CALLAHAN: I think that's every state's fear, is that you have something that you can't see, that you can't put your hands on, that time bomb sitting out there that you don't know about. It's not because of lack of effort; it's not because you're negligent. You're out here doing everything that you need to do, and at that unforeseen something that blows up that you have absolutely no idea that it's going to happen.

BETTY ANN BOWSER: In fact, according to a 2001 federal government study, in-depth inspections like these are "unlikely to correctly identify many of the specific types of defects" that they are looking for. And the Federal Highway Administration report found that, in the case of welding point cracks, where whole sections of bridges are held together, the inspectors correctly identified them in only 3.9 percent of the time.

It was a bridge collapse in 1967 over the Ohio River that led to the creation of the current nationally mandated bridge inspection program. In that tragedy, 46 people died. The Department of Transportation has ordered a top-to-bottom review of that program.

JOHN MYERS, University of Missouri, Rolla: There's human error involved in every stage of design and construction, as well as inspections.

New technology for inspection

BETTY ANN BOWSER: Technology being developed by civil engineer John Myers in a lab at the University of Missouri in Rolla could improve the inspection process. These wires make up sensors that can be embedded in the concrete of bridge structures.

JOHN MYERS: There's a lot of different types of sensors that we can install in bridges. There's types of sensors that can sense vibration or movement. We have sensors that can sense deflection or deformation changes, as well.

BETTY ANN BOWSER: What does that mean?

JOHN MYERS: How much a bridge structure, let's say, deflects under load or traffic.

BETTY ANN BOWSER: All these indicators feed back into computer equipment that put out readings on how the bridge reacts to movement, load, stress, and perhaps one day could prevent another tragedy.

Myers and his colleagues have installed many of these devices in demonstration projects throughout the state. They've also developed bridges with no steel components, using composite plastic materials that can extend the life of bridges by up to 50 years.

This small bridge in a quiet residential neighborhood near the university is an experimental structure. It was built from this prototype in Myers' lab.

They're basically driving over composite plastics?

JOHN MYERS: That's correct, it's a form of a plastic.

BETTY ANN BOWSER: A plastic bridge?

JOHN MYERS: In conjunction with concrete. The concrete takes the compression, and this grid system takes the tension in the lower portion of the deck system.

BETTY ANN BOWSER: The composite plastics will not rust or corrode like steel does from run-off and from salt being poured on bridges in wintertime, but the new materials can be more expensive. Many states like Missouri have budget problems just fixing the bridges they already have, so the technology is not in widespread use.

CARL CALLAHAN: You know, I would really like to have a Lexus, but I'm going to go buy a Hyundai. You look behind, you have a two-lane roadway with high traffic volumes, OK, and you have an old bridge. And if you only have $5 million, where are you going to put it?

Inspecting structural deficiencies

BETTY ANN BOWSER: One of the old ones competing for money is the historic Devil's Elbow Bridge in a picturesque area of the state. Like 7,300 other bridges in the state, this one is rated "structurally deficient." It is in such bad shape it has a load limit, which means big tour buses and large trucks are no longer allowed to cross it.

University of Missouri, Rolla, engineers Genda Chen and Lokesh Dharani pointed out deficiencies underneath the bridge: rust, cracks, corrosion, and of great interest, a gusset plate problem.

GENDA CHEN, University of Missouri, Rolla: The so-called gusset plate is holding several steel member together so that they can work together.

BETTY ANN BOWSER: And, again, the members are what support the bridge?

GENDA CHEN: Yes.

BETTY ANN BOWSER: That's got a hold in it, and it holds up the supports.

GENDA CHEN: See, the member is like -- all the members together is like the skeleton of your body. And the gusset plate we're talking about is like a joint between part of a bone. If the joint has a problem, of course you cannot -- the skeleton system cannot work very well.

BETTY ANN BOWSER: Dharani spotted another potentially dangerous problem.

LOKESH DHARANI, University of Missouri, Rolla: The concrete has fallen off. This is falling, or delamination, and the steel members now are exposed to environment, and they corrode.

BETTY ANN BOWSER: And that makes the bridge weaker?

LOKESH DHARANI: Definitely.

BETTY ANN BOWSER: And is this a fairly typical problem you'd see in an aging bridge in America today?

LOKESH DHARANI: Yes, definitely.

BETTY ANN BOWSER: Rural bridges like Devil's Elbow have to compete with big city bridges, like those in St. Louis, for limited state funds. And St. Louis, a river city, needs bridges to function. Many of them are old. This one was built more than 50 years ago; another is over 100 years old.

Civil engineer Allen Minks worries what the city will do without more major financial support to fix its aging structures.

ALLEN MINKS, American Society of Civil Engineers: I do think we're flirting with disaster. And it's very tragic that, you know, the bridge had to collapse up in Minnesota to draw attention to this, but there's a need for people to be aware of how bad our infrastructure is and that it's not going to go away. It's just going to get worse.

BETTY ANN BOWSER: Even with millions of dollars in improvements to bridges in the St. Louis area in the 1990s, the state still ranks fourth in the nation in the number of structurally deficient bridges.