Thursday Throughput: Collapsing Bridge Edition

[ThTh1] In 1993, Amtrack’s Sunrise Unlimited train derailed at the Big Bayou Canot Bridge, killing 47 people. Investigation showed that a heavy barge had turned up the wrong branch of the Mobile River and struck the bridge, deforming the track and pushing the bridge out of alignment. Later investigation showed that the barge pilot had not been adequately trained.

This was the first thing I thought of in the wake of this week’s Francis Scott Key bridge disaster. As you’ve no doubt seen, the bridge was struck by a cargo ship that was losing power and control in the minutes before. The collision destroyed one of the two piers holding up the main span of the bridge, which immediately plunged in the water, both destroying the bridge and blocking one of the most critical ports on the East Coast.

This sort of thing is rare but not unprecedented. Apart from the Big Bayou Canot disaster, there have been multiple incidents of boats hitting bridges and destroying them. Just a month ago, a barge smashed into a bridge in China, dropping one span into the water and killing five people. In 1983, the Ulyanovsk rail bridge was hit by the Aleksandr Suvorov, cutting the top of the ship, dropping a rail car onto it and killing nearly 200 people. In 1993, the Claiborne Avenue Bridge was destroyed by a tugboat. Probably the most direct parallel is 1980’s Sunshine Skyway Bridge disaster. A large cargo ship collided with a suspension bridge’s support column during a storm, sending a large span into the water and killing 35 people.

In the wake of the disaster, there’s been a lot of irresponsible speculation about what happened and the usual suspects running around either claiming conspiracies or some indictment of the government, corporations or both. So I thought I’d turn a scientific eye to this and explain, in layman’s terms, why a ship was able to take out such a massive and critical bridge.

Here is a short list of things that did not destroy the Francis Scott Key Bridge:

• Diversity, Equity and Inclusion initiatives.
• Terrorists.
• Joe Biden.
• Pete Buttigieg
• Illegal immigrants.

Here is a list of things that did:

• Physics.

The MV Dali is a gigantic ship, nearly a thousand feet long, just shy of Chrysler Building in length, and with displacement of 146,000 tons. At the moment it hit the bridge, it has a speed of about 8 knots. The kinetic energy it delivered in that shot burst of time was the equivalent of a precision hit from a thousand pound bomb, all directed in one direction against a support beam. Very few structures would hold up under that strain, which is why modern bridges have structures intended to divert an out-of-control ship away from piers.

As explained in the Washington Post (gift link):

When a vessel as heavy as the Singapore-flagged Dali crashes with such force into one of the span’s supercolumns, or piers, the result is the type of catastrophic, and heartbreaking, chain reaction that took place early Tuesday.

“If the column is destroyed, basically the structure will fall down,” said Dan Frangopol, a bridge engineering and risk professor at Lehigh University in Pennsylvania who is president of the International Association for Bridge Maintenance and Safety. “It’s not possible to redistribute the loads. It was not designed for these things.”

Bridges, especially long suspension bridges, have to be built a certain way, lest they suffer the fate of the Tacoma Narrows Bridge. For example, the sides can not be solid walls of concrete or steel, because that diversion of the airflow might cause the bridge surface to twist and buckle. They are designed to work with weather conditions and airflow, not fight it. And that means a certain lightness and flexibility. The cost of that is that if a massive ship hits one, the bridge is in serious trouble.

To overcome this, modern bridges are built with concrete piers, artificial islands or structural “dolphins” surrounding the supports that can deflect or absorb the impact of a wayward ship. In the picture below, you can see the old Sunshine Skyway bridge below and the new one above, with the white circular dolphins around it to protect the critical structures. Many old bridges are now being retrofitted with such things; the Key Bridge was not. And I think the wisdom of these expensive and time-consuming retrofits was just proven.

There are other factors at play here, of course. The tugboats left the MV Dali while she was still inside the harbor, increasing the danger of an out-of-control ship. And there may be some corporate corner-cutting involved in why the ship failed at all. But the problem here is fundamental. Our global economy depends on moving massive cargo ships all over the globe. Inevitably one of them is going to crash into something¹. But it turns out we can protect our bridges from this danger. And I think we all just saw, in that horrifying video, that doing so is worth every penny.

In the meantime, spare a prayer for the construction workers who were killed when the bridge plunged into the river. And let’s acknowledge the ship crew who radioed that they were in distress and the cops who stopped traffic going over the bridge within moments of getting that call. Because this could have been far worse if not for their quick thinking and heroic actions. This is the sort of disaster people train for and almost never have to deal with. Thankfully, in a moment of crisis, they responded in exemplary fashion.

[ThTh2] Has the FDA vindicated the use of ivermectin to treat COVID? No. They agreed to take down a few tweets in return for dismissing a lawsuit. On the one hand, I agree with the linked article that doing so was a political mistake by the FDA, giving an apparent victory to the ivermectin quacks. On the other hand, it is hilarious to me that after all their cries of censorship and oppression and murder by the FDA, they settled for … deleting three tweets.

[ThTh3] It’s behind a paywall but Gregg Easterbrook has a great article about Elon Musk’s Starship, which just performed it’s third successful failure launch. He contrasts NASA’s approach to rocketry — which does not allow for failure — against Elon’s, which results in rockets occasionally exploding but is ten times cheaper. If Musk really can get the cost of going into space down to $100 a pound — a goal that seems within his reach — a trip to space could cost you less than a new car. And, for me, it would be a big incentive to lose weight.

[ThTh4] Did “they” lie to you about the COVID vaccines stopping transmission? The answer is complicated but basically no. They were every effective against the original COVID-19 strain and retained modest effectiveness against later mutations. A universal COVID vaccine could, if taken up by enough people, apply the brakes to this virus, which is still killing people.

[ThTh5] The Event Horizon telescope has revealed that black hole at the center of our Galaxy has a power magnetic field.

[ThTh6] Speaking of vaccines, a new one might cure autoimmune diseases.

[ThTh7] Did Tennessee just try to ban chemtrails? No. If you read the article, you’ll find the legislature has passed a bill to ban geoengineering experiments to combat global warming, which is a actual thing, and the press has confounded that with chemtrails conspiracy theories.

[ThTh8] Has the universe been shown to contain no dark matter? Color me extremely dubious. This is the same “tired light” hypothesis that has been used, among other things, to claim the universe is twice as old as we think it is. There is no evidence that tired light is a real thing. There is plenty of evidence that the expansion of the universe and dark matter are real things.

[ThTh9] I have not one video for you this week, but two! The first is looking at aliens through the lens of Spielberg:

The second is looking at how movies handle eclipses, like the big one coming up on April 8.

1. Or get stuck in a canal