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Irma threatens integrity of deficient bridges

September 10, 2017 at 5:14 PM EDT

HARI SREENIVASAN, PBS NEWSHOUR WEEKEND ANCHOR: Among the many structures at risk from Hurricane Irma are Florida’s bridges. Seventeen percent of the 12,000 bridges in Florida are rated, quote, structurally deficient, or functionally obsolete, according to the Federal Highway Administration.

USA Today reporter Brett Murphy is covering that part of the story, and joins me now by Skype from Naples, Florida.

Brett, first of all, these are not Golden Gate Bridge size bridges we’re talking about, but define those terms for me. What makes something functionally obsolete or structurally deficient?

BRETT MURPHY, REPORTER, USA TODAY: Yes. So, most of those are functionally obsolete, and that means, it can be a range of things, but, you know, it boils down to the fact that they need to be repaired or replaced within six years they like to say. And that can mean just that the road is too narrow. The bridge is too wide. It might not be tall enough. It might not have adequate water drainage.

There is a lot of little things that could make it functionally obsolete. A lot of times it affects older bridges. A much smaller percentage of them are what’s called structurally deficient.

Structurally deficient is more serious. There’s far fewer bridges that are structurally deficient but those ones need to be fixed or replaced a lot sooner, and they could have some crumbling infrastructure. They might be unsafe, but most of these bridges aren’t necessarily dangerous or unsafe, but what could make them dangerous or unsafe is a huge hurricane.

All right. Let’s talk about how hurricane impacts a bridge’s structure and makes it more dangerous. I mean, we’re, on the one hand, we are used to seeing water. Water usually flows over. But then, what about the pressure from underneath?

MURPHY: Yes. So, that’s the big concern, especially with a storm like this with such a large surge potential, it could raise the water level beneath the bridge up to five, 10, 20 feet, which is what happened with Hurricane Katrina, which devastated dozens of bridges in the Mississippi Delta. What happens is the surge creates a pocket of air beneath the bridge, that pushes the water upwards, and the bridges aren’t meant to take that sort of anti-grant force. So, the bearings underneath that bend upwards and upwards until they break, or they can just overturn completely and the bridge will literally twist and topple.

SREENIVASAN: And the drainage systems, even those tiny things that you talk about, that ends up impacting a bridge’s integrity?

MURPHY: Exactly yes. So, the structural integrity of the bridge is only as good as how it’s able to pass water beneath it, and if there’s problems draining water either from the road or from under — from the sides, then that bridge can be much more susceptible to crumbling or from that water pressure I was just talking about.

SREENIVASAN: And a lot of these barrier islands, this is the only way you’re going to get on and off these islands, right? I mean, these tiny little bridges that might be older?

MURPHY: A lot of neighborhoods are kind of cut off from the mainland, except for one of these really small bridges, a lot of times, they are very old, a lot of the Miami historic bridges have been there for about 100 years. And these connect just neighborhoods or beach communities and that they’re really only way of passage on to the main land and they’re susceptible. And they may not be huge or long, maybe just, you know, one block long bridges, but they are really important for first responders after the storm.

SREENIVASAN: So, I imagine that cost is a factor in why all these don’t get fixed in one fell swoop.

MURPHY: Yes. You know, Florida is actually really on top of it compared to a lot of states, given a number of bridge — there’s 12,000 all over the state, and the Department of Transportation here has done a good job of keeping up with the major bridges, especially like seven-mile bridge connecting the Keys. A lot of them in Tampa Bay, and Cape Coral, a lot of the main bridges that, you know, the arteries that first responders are going to need have been checked and have been inspected and not up to code.

But there’s just so many of those small ones that it’s a really hard task for FDOT to keep up with all the repairs and replacements for deficient bridges all over the state. That’s what the problem is.

SREENIVASAN: All right. Brett Murphy of the “USA Today” joining us from the exercise room of a firehouse where he is sheltering in Naples, Florida — thanks so much.

MURPHY: Thank you.