The video is surreal, it looks like it barely bumps the bridge and 2 seconds later the entire thing is gone. I don't know what I was expecting, the bridge just looked extremely fragile, makes me wonder what other bridges are at risk of an event like this.
It's not the impact, it's the fact that it just keeps pushing. Movies commonly use slow motion and time extension via editing for destruction scenes because (as we've just seen) real time doesn't always look impressive to the untrained eye.
Also, there's a lot of mass concentrated in that ship. It's the equivalent of hitting a window with a sledgehammer. Small recreational vessels could probably crash into those pylons all day long.
Indeed, the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material, which means the whole bridge bent until the deflection exceeded the tensile strength of the material. A missile impact with the same total energy would exceed impact strength and would probably have destroyed only part of the bridge.
Did the math, this seems surprisingly spot on, at least from the energy perspective. 100k tons going 7.5 kts is about 160kg tnt equivalent which is a little less than the explosive power of a Mk83/GBU-32, probably not enough to take down an entire bridge, just one span if you're lucky. That said, the issue is the bomb expends most of its energy moving air around, the freighter expended nearly 100% of its energy on the bridge.
There's also the loads are balanced on the pylon. When the collapse took out the bridge on one side of the pylon, the other side failed as well. You can see that in the video as the bridge on the right side of the pylon is no longer counterbalanced by the bridge on the left side, and collapses.
Imagine you're holding up a barbell with heavy weights at each end. If the weights on one end drop off, the bar will tilt strongly in the other direction, dropping the weights off on the other end.
Thank you for breaking it down like this. As someone without an engineering background, your explanation (along with some Googling for terms and definitions) really helped me grasp what happened.
You got me wondering:
> the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material
When I first read this, it initially threw me off. The cargo ship's impact not exceeding the strength of the bridge sounds like a positive thing, but upon closer reading of your comment, it sounds as if it was the catalyst to the entire bridge collapsing.
So, how do engineers balance these properties of impact strength and tensile strength, especially considering large ships channel through these bridges near their pylons frequently? How much engineering goes into the possibility of large structures hitting their pylons?
> The cargo ship's impact not exceeding the strength of the bridge sounds like a positive thing, but upon closer reading of your comment, it sounds as if it was the catalyst to the entire bridge collapsing.
I had intended to add that exceeding the impact strength typically results in a local failure near the impact point. A tensile strength failure could happen far from the load and so could be more catastrophic.
I'm not sure if it would have made a difference in this case though, as destroying a main pillar by exceeding impact strength would have by itself transmitted most of the full bridge load to the remaining pillars and that alone may have been enough to exceed the safety margins on the tensile strength that are built into all structures. Unclear without more data, but there was a chance it could have survived in that case, but no chance with the ship consistently applying more and more shearing load.
> How much engineering goes into the possibility of large structures hitting their pylons?
Good questions, I'm not familiar enough with it to provide any further insight, except to say that I believe this bridge was designed long before these huge container ships existed. If they factored ship collisions into the bridge's design constraints at the time, they've no doubt been dramatically exceeded with these huge ships.
I don't think impact strength is factored very much into static structures, tensile strength is more important. It only comes up in very unusual situations like this or 9/11.
Bridges were not designed for being hit. They were designed to span. If those designing and engineering it had considered an impact, the design would not be catastrophic but rather sectional. If sectional, each span would remain standing rather than collapse like dominoes. It takes 3 miles to stop a 100k ton stacked container ship. The things nobody has mentioned are: Current direction and speed. Wind direction and speed. The entry of the vessel in relation to the bridge. The fact that dragging anchor would have on the starboard side pulled the bow right into the pilon, the worst case.
That ship had a 10,000 TEU capacity and was actually hauling a little under 5,000 TEUs. An empty container weighs a little over 5,000lbs, and a full one can be up to 67,000lbs.
If you do the math, you find that it’s just an astronomical amount of momentum, and there’s no effective defense for a bridge that needs support in more than 30 or so feet of water.
Throwback to the scene in The Day After Tomorrow where the cargo ship comes to an almost instant halt after impacting a bus wreck under water. For some reason it managed to stand out as ridiculous even in that movie.
I just saw in a YouTube video yesterday that they actually built a full-size model of the ship (or at least the bow area) and the bit of town it hit. The director didn’t want to use CGI or miniatures.
He spent a full quarter of the movie’s budget on that one scene.
there’s no effective defense for a bridge that needs support in more than 30 or so feet of water
You put in sheet piling 50 meters upstream, and you fill the box with rocks. That's state of the art practice, nowadays, but that bridge was 50 years old.
In 1977 (and in 1972, when construction began), vessels of this size did not exist, and certainly were not allowed in the harbor[1]. But over time, they were given authorization, despite the fact that they could collapse the unprotected bridge like a load of toothpicks.
The real crime here is that there was no retrofit to protect the pylons. It was almost certainly considered and rejected due to cost.
The Oil Tankers of the 70s were the largest vessels ever built. Today the largest container vessels are starting to creep up to their size, but not weight.
The container vessel in question is tiny compared to e.g. the Seawise giant or Batillus Class.
If Baltimore had been anticipating VLCC traffic in the 70s, then presumably the bridge would have been built accordingly and this incident would not have led to a collapse.
According to the marine traffic track shown in the YouTube analysis above, the ship looks to have been heading through the channel, but then nosed in right under the bridge. Would have sailed right past upstream dolphins, and rammed the pylon from the inside anyway.
the modern practice is layers of defense; in addition to building a bridge that doesn't fail at a single point of failure, you also generally design what's around a bridge pier to stop or at least slow down the ship (by, say, running aground onto a bed of rocks around a pier)
"A notable example of dolphins used to protect a bridge is the Sunshine Skyway Bridge across the mouth of Tampa Bay. In 1980, the MV Summit Venture hit a pier on one of the bridge's two, two-lane spans causing a 1,200-foot (370 m) section of the bridge to fall into the water, resulting in 35 deaths. When a replacement span was designed, a top priority was to prevent ships from colliding with the new bridge..."
The MV Summit Venture was a 33,900 deadweight tonnage ship. MV Dali was a gross tonnage of 95,128. Nearly 3× as large. It's questionable whether dolphins would have totally prevented such a tragedy.
Yet similarly, expect dolphins to be brought up as a key component of resiliency for any designed replacement bridge.
Jeasus - seriously - if that was an inbound shipment then it would be worse - this appears to have been leaving - which would infer that the TEUs were more empty than full.
North America has lots of land and oil. Timber (Canada), plastics, and corn fertilised by nitrates that were made using fossil fuel energy. Corn probably doesn’t ship in containers but corn-fed beef and poultry do?
Some import products are crazy cheap because cross-planet shipping is basically free because it's the reverse end of a trip carrying valuable stuff. But they mainly applies to ships returning from low development level regions.
While the majority is bulk, the US does export a lot of industrial machinery. It's just not stuff you normally think about - like the large hvac systems on the roof of large buildings or the caterpillar earth moving equipment/parts to make roads.
Apparently, I was wrong - they are reporting it as a "fully loaded" -- but that does not mean the TEUs were full of goods and services... but thats what they are calling it. So I have no Idea.
Unless ImportYtei.com can get the bills of lading for that ship....
You put it ahead of the pylon so that even when the dolphin or bollard is destroyed, it redirects the ship to—at worst—a glancing blow with the pylon.
You don’t need to dissipate every joule of kinetic energy in the vessel. You just need to redirect it away from the pylon. That horizontal component can be done with bollards and dolphins sufficiently that even a relatively direct original angle should only damage the fenders. From what I see, there were zero such protections around this bridge.
Nothing can protect against a direct hit. But most hits aren’t direct, and those can be redirected without catastrophic pylon failure.
It's somewhat counterintuitive how much energy can be in something moving so slowly. I say somewhat, because when you're up close it's much more obvious, but you're right that on a video it doesn't look like much.
This disconnect happens with boats quite a lot. For example, I can, by myself, pull a 45 foot grand banks trawler in shallow water. I know because I've done so.
But at even very low speeds, I cannot stop it from hitting a pier. I have not tried to do this, but every harbor master has a bunch of stories about people trying to do so and getting a leg or an arm or something squished and pulverized.
People who are not boat people rarely recognize these sorts of dangers, which is why so many get hurt on boats. "I can push us off the dock, so I can definitely keep us from hitting it." Nope, Sir Isaac Newton says you're wrong.
To anyone reading this who isn't an experienced boater:
If you are invited onto someone else's boat, sit down and shut up during docking, don't talk to friends, let the captain concentrate. Don't help, if the captain wants you to do something, they will let you know. If you think you know better than the captain, and this advice is unknown to you, you don't know better. Being a good guest during docking shows experience and helps get an invite back.
Try docking a sailboat on a river. Then slow isn’t an option, since the current will sweep you away in a heartbeat. The key here is planning ahead, including a plan for what to do when you don’t get it right. And you won’t, on the first couple of attempts. I’ve seen it in action, totally hair raising to watch.
This is great advice. For myself, docking in windy situations can be nerve racking. The old adage is to only dock as fast as your willing to hit the pier, and for me this means slow as hell.
I always let guests know exactly what I want them to do, and to your point, it's mainly to sit tight and let me focus.
Similar to stay quiet if the car is about to merge into traffic. But with a boat the stakes are 100,000 times greater due to the huge momentum and that it would be gliding and not slowing down like a wheeled vehicle on land.
Landlubbers are accustomed to momentum (p = mv) behaving in a certain way instinctively from years of experience, where the heavier something is, the more frictional force against it from the ground, and therefore the mass behaves a certain way. This breaks down once the expected friction changes a lot, e.g. trying to stop a moving car or, like you said, a boat in water. I'd imagine it's the same thing in space, where a slowly-moving but massive object would surprise someone at their inability to stop it.
This hit me a a bit ago - you can't really tell how big ships are if you just see pictures of them on sea. I recently hit this in real life. Yeah it's a ship. Oh. It's like 3 - 4 times as tall as I am above water. And it goes 2-3 stories down. And holy hell, a crows nest 30 meters up is... really high up?
And we got the good tour, because we had a severe storm warning as we visited that ship - the kinda storm in which gusts stop you in your tracks and forces you to lean into it to not fall over. Was a great experience. I wouldn't want to be up there with that kinda wind.
And this was a medium sized clipper, somewhat on the small size.
And based off of that, I kind of want to see a retired battleship or an aircraft carrier. Because now I have an idea of how dumbfounded I'll be at those kinda dimensions. It just doesn't appear that big on photos!
The best place I've seen huge ships is Hamburg. People sit and picnic on beaches along the river in the summer, and enormous container and car carrier ships go past.
We had a team we work with a lot over here in HH and went on the treasure hunt on the Rickmer Rickmers as an event. That was very nice - they spread a bunch of little puzzle boxes across the ship so you can search for these, walk through the museum and look at stuff. And the puzzles were neat as well - you'd use the compass the actual helmsman used back in the day to figure out where east is to find some clue, count pests in cargo and such. Very recommendable and a lot of fun.
We just didn't climb up the ropes in winds that almost pushed you over on foot, haha.
The same go for cars. I was hit by a car which was already slowing down but over ran the line and hit me. The car couldn't have been going more than 10 mph but it was enough force to fracture my knee (the fracture type is also colloquially known as a bumper fracture).
But in this case with slow speed, it's the massive (literally) amount of mass of the cargo ship that gives it an un-intuitively large amount of energy.
To your point, it is mass. Most people don't understand mass on water. At 1 knot the ship would do the exact same damage, topple the support and drop the bridge.
Nitpick: squaring makes numbers greater than 1 bigger, and numbers smaller than 1 smaller. In this case we're squaring something with units, and we can't say the input is greater or smaller than the output, because they have different units. What we can say, is that v^2 curves upward: it grows faster with increasing v, and slower with decreasing v.
When you play about with game engines long enough, you start to realise that momentum is the key metric to track rather than speed. Especially in water magnitude can be very deceiving but to give some quick math, this vessel had a momentum at impact of about 154,000,000kg⋅m/s. For a car to have equivalent momentum it'd have hit the bridge at 156,580 mph. Humans are just less adept at appreciating mass vs velocity.
On the other hand, if I were hit by a loaded shopping cart at 3 mph and I weren’t allowed to move my feet, I’d probably be okay if I saw it coming.
Keep the same momentum but scale the mass down to, say, 200g. Now it’s supersonic, and it will hit with maybe 10x the energy of a musket ball. This would be extremely damaging and likely lethal.
(If you make the mass too small, it might go straight through a person, in which case not all of the energy is delivered.)
But the point was that if you were hit with a full container ship at 0.1 mph and not allowed to move you'd be dead.
The only reason why a high energy but slow moving object (thus high momentum) is harmless is that it will deliver a small acceleration to you and you won't suffer from the consequences of a high acceleration (which is what generally kills people when they hit something like the ground at high speeds). But that assumes that you're free to be accelerated and move away.
I think this is a bit too simple. People can get injured and objects destroyed in multiple ways. For example:
One could be torn apart. If you are glued to the ground and you are pushed away with too much force to resist, you have a problem. You can stretch or move a certain distance and withstand a certain force while doing so, and the product of those numbers is the energy you can remove from the thing hitting you. If the impactor is at a fixed speed, then you can turn that momentum into an energy, but that’s a bit silly. You really can stand still and deliver more stopping impulse to an object moving toward you when it’s moving slower because you can resist for a longer time.
One could collide with an effectively infinitely massive object. But the momentum of that object seems irrelevant — hitting a brick wall on wheels at 25 mph seems much worse than hitting the Earth at 0.1mph despite the Earth having many orders of magnitude more momentum. The impact velocity seems more relevant.
One could get hit by a fast-moving projectile. This is complicated, and neither momentum nor energy seem like sufficient measures. As an extreme example, ultra-high-energy cosmic rays surely hit people on a somewhat regular basis, and I’ve never heard of anyone noticing such an event, despite the energy involved being quite macroscopic.
Hm. I'm no physicist but I think your math is off. Remember it's velocity squared. Your car going that fast is has more than a kiloton of TNT or approaching 5 terajoules of energy... that can't be right.
For a 2 tonne car, my very rough math puts it at more like 2100 mph.
I can't edit my post now, but to be clear I was talking about kinetic energy. I would have thought momentum is not a very useful thing to talk about in a case like this where there was some pretty obvious transformation of energy into damage, etc.
As I said though, I'm far from a physicist so happy to be schooled if I'm way off...
> I don't know what I was expecting, the bridge just looked extremely fragile, makes me wonder what other bridges are at risk of an event like this.
The bridge style in question
> Conversely, continuous truss bridges rely on rigid truss connections throughout the structure for stability. Severing a continuous truss mid-span endangers the structure. However, continuous truss bridges do not experience the tipping forces that a cantilever bridge must resist because the main span of a continuous truss bridge is supported at both ends.
cable stays are also generally more popular these days because of the differences in material. All other things being equal, concrete is generally a lot cheaper than a steel truss bridge these days
If they play the cards very carefully, they can pull out and recycle all the steel of the old bridge, and use that to pay for a new (cheaper) concrete bridge.
I remember when I was a kid, I left a bus, and the bus started moving, and I, not being intimidated by the bus moving very slowly (somewhere between 5 and 10 km/h), didn't move a safe distance away from the bus. I think the bus, due to the nature of its maneuverability, had its tail moving not in parallel to me but slightly towards me - so when it has "touched" (hit?) me, even though I thought it was just sliding in parallel, the force was so strong I made a full 360° turn - and I was a tall and chubby boy.
I ended up with no injury, not even a bruise as far as I can remember (who would count bruises as a kid), but definitely with an intuition to respect mass.
> I don't know what I was expecting, the bridge just looked extremely fragile
The strongest man in the world probably seems pretty solid. Put him at the bottom of a 3 degree grade and release the brakes on a full tractor trailer and he'll seem fragile too.
Probably most of them. A structure like that not designed to bear vertical loads, not lateral ones, other than high winds.
The knee is like this too. It lets you stand, run and jump just fine, but you can knock down an opponent with a relatively mild lateral impact to the knee.
Much more of the bridge collapsed than you might think, though, far from the impact.
Bridges are design to withstand a very predictable type and direction of force. It can withstand the lateral wind, but imagine how much force a fully loaded cargo ship can put into it. Once one segment gone the rest is history, because makes the who construction imbalanced.
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