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Engineers have much to consider to plan for rebuild of collapsed Baltimore bridge

DEBBIE ELLIOTT, HOST:

Maryland is getting $60 million in immediate federal aid to begin the process of rebuilding the Francis Scott Key Bridge. Maryland Governor Wes Moore warned of a very long road ahead. Much of the mile-and-a-half-long bridge collapsed earlier this week when it was hit by a large cargo ship. The bodies of two construction workers, who were working on the bridge, have been recovered. Four others are missing and presumed dead. Speaking on NPR's All Things Considered, Baltimore Mayor Brandon Scott expressed frustration at people speculating about how easily the bridge collapsed.

(SOUNDBITE OF ARCHIVED NPR BROADCAST)

BRANDON SCOTT: I think everyone has to stop playing bridge engineer on social media and on TV and on radio and understand that no bridge that I know of is prepared to take a direct hit traveling as fast as that vessel was traveling.

ELLIOTT: For insight from a real engineer, we called Sebastian Bryson. He's the chair of the civil engineering department at the University of Kentucky. I began by asking him what engineers will need to know about the state of the collapsed bridge before officials can even think about rebuilding.

SEBASTIAN BRYSON: As far as the bridge itself and doing the forensics on the bridge, we will have to know the failure mechanisms. How exactly did the bridge fail? Did it fail because the members themselves broke? Or did it fail that the connections, you know, gave way? So that's the first thing - because that tells us that if it were something that it was like, OK, it was - the force of the impact caused the members to break. And so, therefore, the bridge was in fairly good repair. But, now, if it was something like the connections broke because of, say, age and wear and tear, then we need to know that so that as we inspect our current bridges, we can know to look for those types of precursors to see if there's something that we should be specifically looking for in our existing bridges to make sure that they're in good state.

ELLIOTT: Now, when you think about rebuilding the Key Bridge, are there things that need to be done to prevent something like this from happening in the future?

BRYSON: This is not the first time we've had vessel impacts on bridges. And typically, what we do to - you know, it's kind of hard to say to prevent that. But one of the things that we can do is we can put in these protectors out in the bay. When you see pictures of the bridge before the accident, you see these little, round things in the channel.

ELLIOTT: Kind of like bumpers, maybe.

BRYSON: Yeah, they look like bumpers, but they're not on the bridge themselves. They're out in the channel. Those little bumper thingies are, in essence, called dolphins. Then they - basically they are just big stone and concrete barriers that supposedly the vessels will bump into before they come in contact with a bridge. And they are specifically meant to redirect or deflect these vessels from the path of the supports of the bridge.

ELLIOTT: But are they really big enough to block a ship the size of what that one was?

BRYSON: Not this one, no. No. What you would want is you would want something like that to maybe redirect a vessel. But again, let's be honest, a ship that big - it would have been very difficult to redirect that ship going that fast.

ELLIOTT: Now, do you think it would be quicker to rebuild the bridge with the original design, plus a few safety upgrades, or is it smarter to design something completely new and different?

BRYSON: They will most likely design it with something new. It won't be what it was because the way it was originally built - it did not have a lot of redundancies. Meaning, as you saw, the failure seemed like it was instantaneous almost. It knocks out the pier, and then you had this runaway chain reaction - what we in the business called progressive failure. And it just went bam, bam, bam. So the new replacement bridge will have in much more redundancies, and so it will be different. But it will also cost most likely close to twice as much, right? But that's what happens, as we have thought about and looked about how we changed our bridge design over the last 40 years - 40, 50 years.

ELLIOTT: Any idea of how cost and timeline will be estimated?

BRYSON: The original bridge was built about 47 years ago. It cost about 60 to $70 million to build, and it took about five years to build. Today, you're talking about 350 million to 600 million to replace. And I would imagine, because it's such a critical bridge, it will be most likely fast-tracked. And so it will take probably about two to three years to rebuild.

ELLIOTT: Sebastian Bryson is a civil engineering professor at the University of Kentucky. Thank you.

BRYSON: Thank you very much. Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

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