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Baltimore's Key Bridge struck by cargo ship, collapses

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Re: Baltimore's Key Bridge struck by cargo ship, collapses

#911

Post by naasking »

varrock wrote: post #903
naasking wrote: post #839

Earlier quoted context omitted.

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.

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 stren…

> 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.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#912

Post by EasyMark »

hollerith wrote: post #848
elihu wrote: post #789

Earlier quoted context omitted.

Do big container ships like this typically just have a standard propeller/rudder without some kind of directional thruster to assist in maneuvering? https://en.wikipedia.org/wiki/Voith_Schneider_Propeller

Usually tugboats attend whenever a large container ship enters or exits a busy port, and the tugboats have directional thrusters. Port authorities prefer it that way because it gives them more control (since the tugboats tend to stay in the port).

any idea why tugboats weren't standard issue going out of the port considering the potential damage economic and social of accidentally destroying this critical bridge for Baltimore?

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#913

Post by EasyMark »

killjoywashere wrote: post #879
araes wrote: post #541

Earlier quoted context omitted.

Current personal suspicion after watching your linked video (excellent discussion by the wgowshipping author) is: Catastrophic engine failure (1:24) causing wide scale power loss. No rudder control, rudder drift, and ship alignment drift (1:24-1:25:30) Power restored and ship reengages prop with bad ship/ruddder alignment (1:25). However, ship is now pushing itself into a further bad turn. Pilot likely stomps the bra…

I've driven a number of vessels, ranging from a 17' dinghy to a nuclear aircraft carrier and have a number of friends who have been involved in accidents one way or another. I have personally not had the conn during disaster, but have been an engineering officer and a legal officer responding to them, on my ship. To be honest, steering a ship under most conditions is not hard. The anxiety-provoking issues are 1) poor…

Since you have experience in boats of this magnitude, did it make sense not to have tugs minding the ship until it passes under the bridge since it's pretty obvious through common sense what the alternative is when there is a catastrophic engine failure? Would tugs even help if they'd been around during a catastrophic failure of the boat engine(s) making my question a stupid, ignorant one?

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#914

Post by saulrh »

quasarj wrote: post #788
adameasterling wrote: post #752

Earlier quoted context omitted.

> 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…

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

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!

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#915

Post by snarkconjecture »

sho wrote: post #909
moritonal wrote: post #586

Earlier quoted context omitted.

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.

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.

Momentum is just mv, not mv².

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#916

Post by squigz »

hermannj314 wrote: post #392
ericyd wrote: post #339

Earlier quoted context omitted.

A bunch of people die and this is your response?

There is no reason to expect someone to have a rational approach to transportation-related fatality in any direction. Drunk drivers will kill approximately 40 people today in America. Most people won't care about that or demand a congressional response or blame politicians, etc., so it is no more heartless to not care about a few dead people on a bridge either.

Most people do, actually, care about drunk driving accidents.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#917

Post by rramadass »

bmitc wrote: post #754
jordanb wrote: post #743

Earlier quoted context omitted.

The author GPLed it and put it on the internet at one point: http://martrans.org/documents/2006/safety/The%20_tankership_...

Oh, nice. Thanks for the heads up there and again for the book reference.

See https://news.ycombinator.com/item?id=39836079

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#918

Post by nradov »

MBCook wrote: post #898
araes wrote: post #541

Earlier quoted context omitted.

Current personal suspicion after watching your linked video (excellent discussion by the wgowshipping author) is: Catastrophic engine failure (1:24) causing wide scale power loss. No rudder control, rudder drift, and ship alignment drift (1:24-1:25:30) Power restored and ship reengages prop with bad ship/ruddder alignment (1:25). However, ship is now pushing itself into a further bad turn. Pilot likely stomps the bra…

Admittedly very naive question: would they have an anchor? Would it be long enough to hit the channel bed? Could dropping it have helped prevent, or at least slow down, the ship? Or even if so was it just too late when it all went down and it wouldn’t have made a meaningful difference?

The video linked above shows that the vessel had dropped anchor. However, anchors aren't very effective at that speed. They will just drag on the bottom or the chain will snap. There's just too much momentum.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#919

Post by phreeza »

boringg wrote: post #397

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 forc…

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

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#920

Post by hanche »

somenameforme wrote: post #899
killjoywashere wrote: post #879

Earlier quoted context omitted.

I've driven a number of vessels, ranging from a 17' dinghy to a nuclear aircraft carrier and have a number of friends who have been involved in accidents one way or another. I have personally not had the conn during disaster, but have been an engineering officer and a legal officer responding to them, on my ship. To be honest, steering a ship under most conditions is not hard. The anxiety-provoking issues are 1) poor…

Quite amazing videos. I've no experience in this domain and so it makes me immediately wonder - is there no risk of substantial damage from those ships colliding due to a wave hitting e.g. the smaller ship just right and pushing it hard against the larger one?

I am not an expert, but clearly pilot boats must be built to take a lot of punishment. And they don’t have the mass to damage the big ship beyond the paint layer.
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