The Engineering Behind Why The Bridge In Baltimore Collapsed

11:44 minutes

Early morning, Frances Scott Key Bridge, Baltimore, Maryland, USA, August 3, 1988
The Francis Scott Key Bridge in 1988, 11 years after it was built. Credit: Shutterstock

On Tuesday, a large section of Baltimore’s Francis Scott Key bridge collapsed after an enormous container ship lost power and collided with the structure. Two people were rescued from the water, two bodies were recovered, and four others are unaccounted for and presumed dead.

The structural failure of the bridge, which cut off a key roadway and a major international shipping port, has many wondering why this happened. Does the fault lie in aging infrastructure or in the manner the container ship struck one of the bridge’s main supports?

Guest host Arielle Duhaime-Ross talks to journalist Swapna Krishna about the engineering reasons behind why the bridge collapsed and other top stories in science this week, including rockets NASA is launching during the April 8 solar eclipse, new research about how Homo sapiens traveled out of Africa, and visualizing the magnetic field of the black hole at the center of our galaxy.

Correction: We incorrectly stated on-air, and on this page, that the upcoming solar eclipse is next week. The eclipse is on April 8. Both the audio and text have been updated.
Also, in reference to a study about how climate change may affect the way we keep time, we incorrectly stated that climate change is speeding up the Earth’s rotation. But the study indicates that it is slowing it down. The transcript of this segment has been updated.

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Segment Guests

Swapna Krishna

Swapna Krishna is a journalist based in Philadelphia, Pennsylvania.

Segment Transcript

ARIELLE DUHAIME-ROSS: A large section of Baltimore’s Francis Scott Key bridge collapsed earlier this week after a container ship lost power and collided with the structure. The structural failure of the bridge, which cut off a key roadway and a major international shipping port has many wondering why this happened. Does the fault lie in the initial design, in aging infrastructure? Or is it unreasonable to assume that parts of a bridge or all of it might survive this kind of collision. Here to talk about the bridge’s engineering and other science stories this week is Swapna Krishna, a space journalist based in Philadelphia, Pennsylvania.

Welcome to “Science Friday”.

SWAPNA KRISHNA: Thank you so much.

ARIELLE DUHAIME-ROSS: So tell us what we’ve learned about the bridge’s collapse?

SWAPNA KRISHNA: Well, this bridge collapse is horrifying. I think it triggers something visceral in a lot of us, a fear of a bridge falling while we’re driving over it. And there has been a lot of talk about aging infrastructure, which is an important discussion we need to have in the US. But that’s not the issue in this case.

It’s literally just a absolutely massive ship. It is hard to understand the scale of the Dali. It is 300 meters long. And for reference, the Eiffel Tower is 300 meters tall.

This ship is 95,000 tons when empty– and it was not empty– moving at nine miles per hour. So literally, it hit one of the two key support structures of the bridge and obliterated one and the bridge collapsed. It was not about aging infrastructure. Because of the bridge’s design, nothing could have avoided this.

ARIELLE DUHAIME-ROSS: OK, so tell me more about the bridge’s design. What do we know about that?

SWAPNA KRISHNA: It was a truss bridge. And that means the interconnectedness of its design is what kept it stable. But the weak points were these two concrete piers. And as early as 1980, experts flagged that a direct hit from a heavily loaded container ship would bring down the bridge.

So they have known about this problem for a while. It’s not a design flaw necessarily. It’s just a weakness. But it is important to note that any bridge can collapse. You cannot build a collapse-proof bridge.

But building a bridge like a cable-stayed bridge would reduce that risk especially in the event of another collision like this.

ARIELLE DUHAIME-ROSS: OK, so I’m super pumped about the solar eclipse. I’m already preparing for it. And I hear that NASA has a plan to launch rockets while it’s happening. What’s that about?

SWAPNA KRISHNA: I think this is such a cool story. So yes, NASA will launch sounding rockets into the eclipse to study changes in the ionosphere during the eclipse. And the ionosphere is basically the boundary between Earth’s breathable atmosphere and space about 55 miles to 310 miles above the Earth’s surface.

ARIELLE DUHAIME-ROSS: What’s a sounding rocket?

SWAPNA KRISHNA: A sounding rocket, they’re basically launched in a parabolic trajectory. They only spend anywhere from five to 20 minutes in space. So they’re suborbital flights. These are good options for studying the atmosphere because they can be launched from small rockets that don’t require expensive boosters.

ARIELLE DUHAIME-ROSS: OK, and what does NASA hope to learn from these launches?

SWAPNA KRISHNA: So basically, our ionosphere is always changing. And this area is electrified because what the sun does is it heats up gases in the upper atmosphere. And then they lose electrons. And then the sun sets, the ionosphere thins out because these ionized particles recombine and regain their electrons and neutralize their charges. And then the cycle starts again when daylight hits.

And it’s important to note that things like solar storms and space weather also affect and change the ionosphere. So the idea is studying these changes, especially the sudden changes that will come with the eclipse– because it’s going to have a similar effect as night falling, but it’s going to happen all of a sudden.

ARIELLE DUHAIME-ROSS: OK, so this is just like a sped up version of it where they get to test slightly different conditions.

SWAPNA KRISHNA: Exactly. And what’s key about the ionosphere is it’s important for radio communication because radio signals bounce off the ionosphere. So whenever we have an event like this or a solar storm, radio communication gets disrupted. So part of this is studying how we can minimize these disruptions.

ARIELLE DUHAIME-ROSS: All right. All right, I’m interested in that. Staying in space for a bit, NASA is considering ending operations on one of its satellite observatories?

SWAPNA KRISHNA: Yeah, this is kind of a sad story. NASA is dealing with budget cuts. And so the fiscal year 2025 budget had some alarming news. They’re basically stepping down operations of the Chandra X-ray Telescope, which was launched in 1999.

Chandra is currently the only high resolution X-ray telescope in the world. So this would affect global science. And this telescope is still doing great science is the thing. If it’s shut down, there is no replacement anytime soon for at least a decade.

And Chandra studies things like dark matter, the structure of black holes, stellar explosions like supernova. It’s really important to science.

ARIELLE DUHAIME-ROSS: All right, so we’ll be keeping an eye on that. Coming back down to Earth, it looks like there’s bird flu going around on some farms. It’s affecting dairy cows in the South of the US. What’s going on with that and how worried should people be?

SWAPNA KRISHNA: So yeah, this is kind of the rare bird flu story that doesn’t end in horror. People are probably really familiar with bird flu leading to mass slaughter of poultry. But in this case, it’s not terrible news.

So yes, the milk from dairy cows in Texas and Kansas tested positive for bird flu. The strain is type H5N1. And that can sometimes affect people and that can be a concern. But it’s good news that the specific mutation in these cows does not look like it will easily transfer to humans. So that’s one piece of good news.

The other piece of good news is there is no slaughter required. These cows are getting the equivalent of basically a cold. All this is doing to them is decreasing milk production and lowering appetite. And they recover in seven to 10 days on their own. So that’s very good news for the farmers and the cows as well.

ARIELLE DUHAIME-ROSS: And there’s new research that’s giving us more clarity on how and where homo sapiens lived after leaving Africa tens of thousands of years ago. Tell me about that?

SWAPNA KRISHNA: Yeah, this is super interesting. So just to paint the bigger picture, our species homo sapiens emerged about 300,000 years ago in Africa. And then 60,000 to 70,000 years ago, they migrated to other parts of the world.

But there’s kind of been a lingering question of where they went after they left Africa, but before they moved on to Europe and Asia around 45,000 years ago. So now we have a paper in nature that identifies where that hub was located in what’s now Iran, Kuwait, parts of Saudi Arabia, and the UAE. So basically to do this, they used genetic data to figure out a larger area that homo sapiens could have settled in between these migrations. And then used paleo ecological data to figure out like what would be the most attractive spot for these ancestors?

ARIELLE DUHAIME-ROSS: OK, so the big news there is that this study showed that basically instead of moving around for a while after leaving Africa, homo sapiens stayed in this one major spot for a period, right? That’s the big deal there.

SWAPNA KRISHNA: Yeah, they stayed in one spot and they lived in small bands of hunter gatherers. And because there was a diversity of environments and ample resources in this area, that would have been attractive to them.

ARIELLE DUHAIME-ROSS: And this next story is both fascinating and entirely depressing, but in the nerdiest way. It looks like we’re seeing another unexpected effect from climate change. It’s affecting how we keep track of time.

SWAPNA KRISHNA: Yeah, so as a space journalist sometimes it’s easy to forget that space science and kind of climate change are very connected. And this latest study really emphasizes that.

It’s a paper in nature and it’s showing that the melting of our polar ice caps is slowing down the Earth’s rotation.

ARIELLE DUHAIME-ROSS: OK, and what is the implication for time?

SWAPNA KRISHNA: Basically right now we use the leap second to keep our clocks in sync with astronomical time, which is the precise rotation of the Earth. It’s important for a lot of reasons, including for things like GPS that need to know precisely where and when you are to tell you where you need to go. And in the 1970s, we discovered that the Earth was actually slowing down its rotation because of tidal friction.

And you can think of that as like tides, except all over the world. And to keep our time in line with astronomical time, they added the leap second, which is one extra second at the end of the year. There were 27 leap seconds added between 1972 and 2016. But now the Earth is slowing down.

That’s happening for two reasons. First, meltwater from the poles is making its way to the equator. And so that’s shifting the Earth’s mass. And there’s more of an equatorial bulge than there was before. And then in addition to that, land that doesn’t have ice on it anymore– so we’re seeing Greenland and Antarctica mainly– that’s rising and that’s making the Earth more spherical.

So these two things are actually contributing to the Earth’s rotation slowing down.

ARIELLE DUHAIME-ROSS: Wow, that’s really interesting. What’s the solution to that?

SWAPNA KRISHNA: The paper posits we might have to start subtracting leap seconds from the calendar. But these things can be very hard to predict, so we’ll just kind of have to see what happens.

ARIELLE DUHAIME-ROSS: Ugh, this is so cool and so weird and also so sad that it’s because of climate change. But yeah, definitely some good nerdy stuff. So another cool thing, for the first time scientists visualized the magnetic field of a black hole. What does that mean? How did they do it?

SWAPNA KRISHNA: Yeah. This is really, really cool. So if you haven’t seen the picture, it’s basically this orange photo of a fuzzy black hole with these lines around it. And you can see kind of the direction of movement through those lines. So this is a photo of the black hole at the center of our galaxy called Sagittarius A star.

It’s not a direct image of the black hole because you can’t directly observe a black hole. But you can see the Event Horizon and the bright accretion disk. Now, these lines are magnetic fields spiraling around the black hole. But it’s important to note they aren’t really there as in this is not a direct photo. But scientists observed Sagittarius A star in polarized light and added these field lines over an image from the Event Horizon Telescope.

So basically, we’re looking at the movement of the magnetic field around the black hole at the center of our galaxy. And polarized light is specifically important here because light waves can be oriented in any direction. And when they are, that’s unpolarized light.

So polarized light is when the light waves are oriented in a specific direction. And so scientists used this polarized light to study Sagittarius A star’s magnetic field because it controls the direction the light waves move. And that allowed researchers to measure the structure, strength, and direction of the magnetic field.

And this movement contributes to the emission of jets of matter from the accretion disk of the black hole. And so this tells us that our supermassive black hole may have jets that we don’t know about yet.

ARIELLE DUHAIME-ROSS: Whoa. OK, thank you so much for bringing us these stories Swapna. It was a pleasure having you on the show.


ARIELLE DUHAIME-ROSS: That’s Swapna Krishna, a journalist based in Philadelphia, Pennsylvania.

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