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Comment by boringg | Hacker News Reader

This is a tragedy for those involved.

My rough calculus points that the amount of force of this collision is on par with a large scale natural disaster. Everyone being surprised at the bridge collapsing needs to reconcile with the amount of force that struck the bridge - it is a truly significant amount of Newtons that hit the bridge. More than a train going from full speed to a full stop. Unbelievable amount of force.

I am also a bit surprised at how many people don't grasp this or grasp engineering, magnitude of forces and design principles.

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> Everyone being surprised at the bridge collapsing needs to reconcile with the amount of force that struck the bridge ... I am also a bit surprised at how many people don't grasp this or grasp engineering, magnitude of forces and design principles.

A spokesman for CalTrans claimed today that Bay Bridge could have taken the same hit without damage, thanks to fenders that protects all pylons for all bridges in the San Francisco Bay Area (1). Cargo ships are heavy, yes, but it appears we have the technology to prevent bridge collapses due to these sorts of collisions today.

1. "The Bay Bridge’s fenders insulated the span during the 2007 incident, so that the Cosco Busan ship struck a bumper, never hitting the bridge itself, Ney said. He noted that fenders on Bay Area bridges should be able to handle a ship traveling at 8 knots, the velocity at which the ship hit the Francis Scott Key span."

https://www.sfchronicle.com/bayarea/article/baltimore-bridge...

"A ship traveling at 8 knots" is a meaningless statement. You need to know how bit the ship is...

Container ship

Thanks to things like planetwide bottlenecks through specific canals and locks and design of certain ports, approximately all container ships are within a couple meters of one of only a handful of size buckets, several of which are fairly close to each other besides. For example, a large fraction of the world's container ships are sized to be within a meter of fitting into chinese port facilities and the suez or panama canals. Because these dimensions include the depth of the water as well as the length and width of the ship they also limit the total volume of water which is available to be displaced, which puts a limit on the total mass that can be floated. As a result, "a container ship" is actually a fairly tight and predictable specification of a ship's maximum mass!

That may be so and I appreciate CalTrans confidence in the matter. I however would never want a similar set of circumstances to strike the bay bridge and have to test it.

It is a very different bridge design (assuming were talking about the Oakland to treasure island portion) and it is built in earthquake country.

I'm not saying there shouldn't have been fenders or other protective measures. I'm saying that the amount of force on a direct hit that STOPPED that the ship dead in its tracks - that bridge was not going to withstand it and I do question what would happen to the bay bridge. Again I appreciate the confidence of CalTrans to reassure the commuters but I have seen government officials express too much confidence before.

It's likely that a lot of people don't understand just how huge these ships are. I'd imagine that much of HN doesn't have a ton of firsthand experience with shipping yards or even close friends/relatives that work on these things. In my experience, almost nothing hides just how large it is than a giant ship.

That's fair. If you don't live in a major port city you likely don't understand.

Maybe we should reframe it to a more familiar territory. It could be the equivalent of a second tier unsophisticated, unsuspecting, dated website with a relatively small amount of traffic hitting it being hit by a state sponsored actor DDoS attack and expecting the website to survive.

I'm with you on this one, I grew up around boats and remember the dread of even getting near a containership in a 16 foot Boston Whaler. That fear was more primal and daunting than sailing home during a tornado watch.

My family and I drove through the Ports of LA/Long Beach on vacation last summer. A port is basically an entire city dedicated to getting things in/out of the water. Takes 15-20 minutes to drive through. You can't imagine the number of cranes/lifts. It's worth the drive through.

This ship was carrying ~5,000 TEU (Trailer Equivalent Units). Imagine 5,000 fully packed semi trucks crashing into the single upright of that bridge.

Even at 7.5 knots (~10mph) the bridge stood no chance.

Would it even stand a chance at 1 mph? If not, what is the speed that would make it imaginable for the bridge not to collapse?

When I was a kid, we would go fishing off of pier near a port. The size of carriers and tankers is staggering. And if you get close enough to see numbers and lines near the front of the boat, you realize that fully loaded these things are 30 40 ft underwater.

For an assumption to get a gauge of forces involved: Large cargo ship mass is 190,000 tons @ 8 knots (14.8 kph) - I end up with a Force of about 1.609 * 10^9 or 1.6 GN of force of impact assuming it stopped over a very short distance (1 M).

Force comparables (thanks GPT) for scale: Saturn V rocket thrust is about 34 GN on take off.

Earthquakes: early stage of the earthquake might have about 1 GN of force in build up.

Great pyramid of Giza is estimated at 50 GN of weight - so 1.6 GN could support a fraction of the weight.

Engineering machinery - some of the largest human machines such as mining or lifting can exert forces only in the MN so would need a 1000 machines to get up to a GN.

I've seen a bunch of weight numbers but it's around a billion joules, the equivalent energy to a Mk83/GBU-32 1000lb bomb (200kg explosive fill).

> More than a train going from full speed to a full stop.

I wonder. This ship might have massed about ten times a typical freight train on the heavy side, but the train is going to be moving a lot faster than a ship navigating in port, right?

Is force really the right dimension for this kind of analysis? I was thinking more in terms of energy deposited into the system.

> I am also a bit surprised at how many people don't grasp this or grasp engineering, magnitude of forces and design principles.

Who are you even referring to? Are you just inventing a population of people in your mind to flex against here? Trust me, people get it.

Seems a bit gauche to link to them, but there are comments all over this thread, including top level ones.

And many here have engineer in their job title.

There are a lot of types of engineering, and some of them are VERY far away from civil/structural engineering.

Your last sentence is pretentious and condescending.

To be fair I am truly surprised at the comment thread here and people being surprised that it collapsed and the lack of understanding of magnitude of forces. I always think of HN as a fairly educated group with a large portion of engineers (skewed heavily towards software which doesn't always have a background in the physical environment).

I don't intend to sound pretentious or condescending. Maybe its more that I need to reconcile with my own expectations of the community level of knowledge/domain of expertise.

I rather have a high bar of expectations than a low bar though to be honest.

The absolute mass of container ships are inconceivable by default - it's really worth repeating how much weight and force they bear.

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