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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

#931

Post by JumpCrisscross »

Repulsion9513 wrote: post #626
JumpCrisscross wrote: post #538

Earlier quoted context omitted.

> there’s no effective defense for a bridge that needs support in more than 30 or so feet of water You deflect it. Failing at that, you direct the force into destroying the ship. Of course, the best solution is no in-water pylons. But that isn’t always feasible.

> direct the force into destroying the ship Nice immovable object you've got there.

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.

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

#932

Post by rightbyte »

jack_riminton wrote: post #141
lukan wrote: post #105

Earlier quoted context omitted.

"but could you call it well-engineered" If it is still standing after 1000 years, I would say yes. You cannot build a bridge out of stones with bad engineering - it would collapse under its own weight. edit: does "well engineered" now means over engineered to some?

"If it is still standing after 1000 years, I would say yes" but what if they included far more material in areas where it wasn't needed, skimped on other areas and it fell down tomorrow? It's almost a philosophical question, and it's true that the bridge builders happened across a solid design by accident. But I think the true definition of engineering has to encompass a level of efficiency through design, calculatio…

> and it's true that the bridge builders happened across a solid design by accident.

I think there is a great overlap between "holds for whatever scheme the prefecture will do to test it while I stand under" and "holds for a thousand years".

There is like a limit where fatigue stress stops being a thing in a cycle graph. Many failure modes is due to penny wise cost cutting.

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

#933

Post by reader_x »

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).

If tugboats had been attending Dali, would they have had enough thrust to correct Dali’s course when it lost power?

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

#934

Post by lolc »

hwh47 wrote: post #719
TaylorAlexander wrote: post #66

Somehow I find it surprising how completely the bridge collapsed after the damage. I understand that a container ship collision is serious, but you could imagine a scenarios where the bridge slumps or buckles but doesn’t just disintegrate like that. It’s surprising that ships capable of doing this damage were probably regularly driving past it, and its safety as a thoroughfare depended entirely on those collisions no…

separate but pertinent question: what was the mv dali's air draft? (FSK bridge's clearance is 185'/56m) was the container ship going to fit under the bridge, i.e., perhaps the incident was an aborted attempt to crossing under the bridge?

I'd assume the procedure of how the ship will enter and leave was clear to all involved before it even got close to Baltimore.

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

#935

Post by dredmorbius »

desro wrote: post #421
dgfitz wrote: post #267

Earlier quoted context omitted.

I think 30-35k cars a day cross that bridge. Being local to the area, is is going to make traffic in the entire metro area much worse, and it is already awful.

Report from CBS News mentions the bridge handled "11.5 million" vehicles a day. EDIT: That number seemed fishy; I think the reporter is referring to the traffic along the entire I-95 corridor. https://x.com/CBSNews/status/1772556368106450953?s=20

One way to assess these numbers is to conduct a quick sanity check. How many cars per minute or second would this be?

11.5 million cars/day is equivalent to :

  ~48,000 cars/hour
   ~8,000 cars/minute
     ~130 cars/second
Clearly, somethings ... a tad off.

11.5 million cars per year however works out to:

  31,000 cars/day
   1,300 cars/hour
      21 cars/minute
Or roughly a 3 second headway per vehicle. Given four traffic lanes (two in each direction), that would be a vehicle every twelve seconds per lane, which seems far more reasonable. That's spread out over the day, so peak-hour traffic would be much higher.

Peak capacity for a highway lane is just shy 2,000 vehicles/hour:

https://www.mikeontraffic.com/numbers-every-traffic-engineer...>

Which would put the Key Bridge's maximum capacity at about 192,000 vehicles/day.

For comparison, the San Francisco-Oakland Bay Bridge saw about 42.7 million paid toll crossings. As these are metered only in the westbound direction, actual crossings are likely double that, or 85.4 million/year, or about 230,000/day.

(The bridge sees 1/3 the total traffic of all California state-owned bridges.)

https://mtc.ca.gov/operations/programs-projects/bridges/san-...>

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

#936

Post by OJFord »

rightbyte wrote: post #823
OJFord wrote: post #780

Earlier quoted context omitted.

Well yeah, they were only minutes away at the point they lost power, there was very little time to do anything at all, that's why I asked. Personally I can't really imagine anyone holding it against them for using the 'signal that's for other ships' 'incorrectly' or 'against protocol' in such a situation. I think the comments speculating that the horn is either purely or in some way (e.g. solenoid) dependent on elect…

There is a proper signal. You are supposed to give at least five short signals if you think there is an impeding collision.

Alright well feel free to read my original question as if I knew and meant that then, I don't think I precluded it.

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

#937

Post by hanche »

somenameforme wrote: post #927
hanche wrote: post #920

Earlier quoted context omitted.

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.

I agree that it seems that must be the case. I'm just curious where my assumptions break down - whether I'm overestimating the mass of the pilot boat, overestimating the force a single perfect wave can impose, or underestimating the thickness of these ships' hulls. I've just always be impressed by the amount of energy that boats impart when they collide with anything. Like in this case, the entire bridge was brought…

Well, here’s a story to give you an idea. In November 2018, a frigate collided with an oil tanker on the Norwegian coast. It was only a glancing collision, involving the starboard side of the frigate and the bow of the tanker. The frigate was severely damaged, basically having much of the starboard side ripped open, and it eventually sank. You could hardly see any damage to the tanker. (Luckily, or perhaps miraculously, no one was killed or seriously injured.)

Back to the pilot boat: Steering one in heavy seas when trying to deliver or recover a pilot is clearly a difficult art. But at least in the videos shown, there doesn’t seem to be much of an impact between the vessels. I am sure that is in part due to the skill of the steersman. Besides, I am sure the pilot boat will have permanently mounted fenders all around.

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

#938

Post by fl7305 »

1letterunixname wrote: post #740
fl7305 wrote: post #353

Earlier quoted context omitted.

> when this bridge was built boats that large weren’t a risk Doesn't sound plausible to me. Very large Panamax ships were used in the 1970's when the bridge was built.

Sorry, but you're very wrong. A civil engineer on Sky News even raised this issue. https://www.container-transportation.com/worlds-largest-cont...

Panamax specifications (320 m length, 32 m width) have been in effect since the opening of the canal in 1914. Some ships were already larger than that back then. The Titanic was about that size.

The ship that knocked down the bridge could weigh ("DWT") up to 115 000 tons.

Some ships from the 1960s and 1970s:

Universe Ireland: Launched in 1968, it had a DWT of over 300 000 tons.

Esso Atlantic (1977): DWT of over 500 000 tons.

But these were tankers. You're right that container ships were not as big back then.

One of the larger container ships when the bridge was built in 1977 was MV Hamburg Express. It was 280 meters long, 32 meters wide, and had a DWT of 50 000 tons.

Do you really think a 280 meter long ship weighing 50 000 tons would not have knocked down the bridge in exactly the same way?

https://de.wikipedia.org/wiki/Hamburg-Express-Klasse_(1972)

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

#939

Post by fl7305 »

1letterunixname wrote: post #738
chasd00 wrote: post #312

Earlier quoted context omitted.

I don’t drive boats or around water much but I’ve seen “bumpers” on bridge pylons before that make a collision more of a glancing blow and guide the boat to the side. I guess there wasn’t any installed on this bridge? Also, someone on Imgur pointed out that when this bridge was built boats that large weren’t a risk. That may or may not be true but sounds plausible.

Fenders and such. A major problem is this bridge was designed and built in an era where ships were substantially smaller (3000 TEU) than they are today (20000 TEU).

The ship that brought down the bridge had a capacity of 10 000 TEU. It's max weight (DWT) was 115 000 tons.

There were container ships with a DWT of 50 000 tons when the bridge was built.

There were also tankers with 10x that (500 000 tons), so large and heavy ships shouldn't be a Pikachu-face surprise to the bridge designers. If nothing else, the trend in increasing ship sizes was clear to anyone looking at it.

Do you think the bridge steel pylons would have resisted a 50 000 tons ship plowing into them?

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

#940

Post by fl7305 »

doer1984 wrote: post #688
TaylorAlexander wrote: post #66

Somehow I find it surprising how completely the bridge collapsed after the damage. I understand that a container ship collision is serious, but you could imagine a scenarios where the bridge slumps or buckles but doesn’t just disintegrate like that. It’s surprising that ships capable of doing this damage were probably regularly driving past it, and its safety as a thoroughfare depended entirely on those collisions no…

Ironically, simply bulking up the ground around the piers would have had the ship run aground; at 8 knots the ship would have slowed to a stop within several yards, and suffered minor damage, maybe would have required being tugged back into clear waters. Running aground puts the majority of impact into a downward force absorbed by the earth. It's hard to build a bridge pier that will withstand 200,000 tons of direct…

> simply bulking up the ground around the piers

That is exactly what they did around the pylons of the large Öresundsbridge between Denmark and Sweden.

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