U.Va. Engineering Professor Thomas Baber Assesses Impacts of Minneapolis Bridge Collapse

August 05, 2007

August 5, 2007 — For Thomas Baber, the collapse of the Interstate 35 bridge in Minneapolis last week has two very different implications.

On the one hand, Baber does not want people to panic and worry that every bridge they cross is potentially about to fall. At the same time, he views the incident as an opportunity to raise awareness of the dire need for support to repair the United States infrastructure.

Baber, associate professor of engineering at the University of Virginia's School of Engineering and Applied Science, was in the field, placing electronic monitors on a bridge in Southwest Virginia on Wednesday (Aug. 1) when events in Minneapolis began to unfold.

Thanks to video of the Minneapolis collapse posted on CNN.com and liberal use of the Google search and mapping services, Baber got up to speed on the I-35 disaster in a hurry, forming his own theories of how the bridge had met its demise. By midday, he was fielding media calls.

His message: “My perspective is that this event may call attention on a national level to the fact that the infrastructure is in serious need of help.”

Baber linked the Minneapolis bridge collapse to the July 18 explosion in a New York City steam tunnel that killed one and injured dozens, calling these two events a “wake-up call” that should focus the nation’s attention on the need to maintain its vital infrastructure.

“Right now, we’ve got the country’s attention,” he said. “Everyone wants to know what the civil engineers think. Two weeks from now, nobody will care. We’ll go back to business as usual. Unless something is done while we have the public’s attention, 20 years will pass, there’ll be another failure and everyone will be wringing their hands again.”

Baber emphasized that the Minneapolis bridge collapse and the accompanying concerns about bridge safety should not be blown out of perspective. It is still the case, he emphasized, that motorists run a far greater risk from other motorists than from a bridge failure.

Yet, he does believe that because infrastructure — roads, bridges, drinking water systems and other public works — can be a less exciting topic than many of the high-tech advances that captivate us, priorities may be skewed.

"Infrastructure should be as high a priority as a lot of the high-tech things that we’re all focused on,” he said.
The I-35 bridge that collapsed is a deck-truss bridge, a common design of bridges built in the 1950s, ’60s and ’70s. Its fatal flaw, Baber said, was its reliance on “fracture-critical members” — pieces that, should they fail, would likely bring down the whole bridge. Newer bridges, like the one in Southwest Virginia where Baber was placing monitors last Wednesday night, are designed with more redundancy, meaning that if one part fails, other parts are able to carry the load.

The I-35 bridge had been labeled “structurally deficient,” as are about 12 percent of the nation’s bridges, Baber said. In Virginia, only about 9 percent of the state’s bridges are labeled as being structurally deficient, and only about 3 percent of its interstate bridges. While those numbers are below the national averages, so were Minnesota’s, Baber said.

Ideally, only about 1 percent of the nation’s bridges should be structurally deficient, Baber said. He estimated that it would take about $70 billion to address the problem of obsolete or deficient bridges nationwide.

“There has to be the money to do it, and there has to be the will on the part of government at all levels — local, state and federal — to support that kind of effort,” he warned.

As to the cause of the I-35 bridge collapse, Baber predicted that investigators would eventually find a fracture either in a steel truss or a connector near the north end of the bridge; he even identified a few specific candidates on a picture he located on the Internet. He said he doubts that construction work on the bridge deck or vibrations from a train passing underneath had anything to do with the collapse, as the deck has nothing to do with the support of the bridge.

It is mildly surprising that the collapse did not happen in the winter, he added, as Minnesota’s cold climate would likely make the metal more brittle then. The failure will likely be blamed on corrosion and metal fatigue, he predicted.

In the meantime, Baber said that it is important for people in his profession to seize the initiative in the coming weeks and make their case for maintaining the nation’s infrastructure.

“There is an ongoing effort on the part of the Department of Transportation to inspect, maintain and repair, if needed, our bridges,” Baber said. “We have techniques available to do this, but there has to be money available on the part of government at all levels -- local, state, and national — to support that effort.”