Sound Engineering: Why the Leo Frigo bridge buckled
Michael Oliva, a professor of civil and environmental engineering at the University of Wisconsin-Madison, is one of the state’s foremost experts on bridges. He has, naturally, been following the Leo Frigo Memorial Bridge in Green Bay Wisconsin, which began sagging in late September. The bridge is among the most important in Wisconsin—it carries a portion of Interstate 43 over the Fox River—so its problems raise concerns about the condition of the state’s infrastructure. In our latest Sound Engineering podcast, Oliva explains why the bridge buckled, and how these problems can be avoided in the future.
Scott Gordon: A lot of people have been asking Michael Oliva what he thinks about the sagging in the Leo Frigo Memorial Bridge, which carries a portion of Interstate 43 across the Fox River in Green Bay, Wisconsin. Oliva, a professor of civil and environmental engineering at the University of Wisconsin-Madison, is a bridge expert and has worked with the Wisconsin Department of Transportation on many infrastructure issues. He says that what is unusual about the Leo Frigo bridge—one of the state’s largest bridges—is what’s caused it to begin sinking in late September 2013. Investigators found that water and soil properties corroded some of the steel pilings that support the bridge.
Mike Oliva: It’s very unusual. I’ve never seen a bridge fail because of the piles corroding. It gives an indication that it’s something that we’ve got to look out for, because it was built on industrial fill, and the industrial fill must have had some corrosive chemicals in it that nobody ever thought of. Any time they go in and they do the borings before they build the bridge, in the borings, you could see, on the plans, that they indicated it was industrial waste, but they never considered the fact that it might be a corrosive industrial waste, I think, because they just never ran into that situation before.
Scott Gordon: Luckily, not very many Wisconsin bridges are built on industrial fill.
Mike Oliva: I don’t think in Wisconsin, probably, we have a lot. There could be some in Milwaukee, because there are certain industrial waste sites, particularly down in the Milwaukee Valley area, and there are quite a few bridges down there, because it was an area where the industry disappeared and there is a nice corridor to build bridges through, and highways. So it could be there. It’s possible, but I don’t think we’ll see too much in other places in Wisconsin, because we don’t have that many big industrial cities where there would be those kinds of industrial waste sites. Chicago, New York—they’re probably starting to think about, “What do we have?”
Scott Gordon: Oliva says he’s not alarmed about Wisconsin’s bridges in general—in fact, he thinks we’re in better shape than most other states. But he thinks this is a good moment to start thinking about how the demands on our roads have changed over the years.
Mike Oliva: We’ve got a lot of trucking in Wisconsin that’s carrying real heavy loads, like turbines, for wind turbines, and these are pretty massive, heavy loads. These vehicles weigh almost five times as much as we use for our design of bridges. But because of the numerous axels on these trucks, the bridges can still carry most of them. We’re all facing the fact our infrastructure’s aging, and it’s aging fast. The whole Interstate system now is over 50 years old, and those bridges have gotten much heavier loading than they were ever designed for.
Scott Gordon: Oliva has been working with the state recently to begin monitoring several of its major bridges and determine how they hold up under these new stresses. He also has some recommendations for how the state can avoid problems like this in the future.
Mike Oliva: In Wisconsin, we use almost all steel piles under our bridges. The steel pikes have no protective coating, really. What protects them is because they’re in the ground, oxygen can’t get to the pile, and if oxygen can’t get to the steel it really doesn’t rust. When you have these corrosive chemicals, there’s oxygen available in the chemicals, so you get corrosion occurring where you never expected it. Now, the unique thing is, Wisconsin uses almost all steel piles, because there’s no manufacturer in Wisconsin that does pre-cast concrete piles. If you go out to the West Coast or the East Coast or down south, a lot of the states put their bridges on concrete piles. If in this situation we had concrete piles in Wisconsin, the problem probably never would have occurred. So I think one of the things that may also come out of this long-term is that Wisconsin may start looking at using concrete piles.
Scott Gordon: For more information on Oliva’s research, look up his faculty page at engr.wisc.edu.