Baltimore's Key Bridge struck by cargo ship, collapses
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Re: Baltimore's Key Bridge struck by cargo ship, collapses
#182Earlier quoted context omitted.
Thanks! So why are huge—ass container ships allowed to navigate underneath fragile public bridges with single points of failure? The not unlikely worst case is that the ship is out of control for some reason…
We notice these type of accidents because they’re so rare. 5k+ people die each year because of large trucks on the road, by comparison, boats and bridges are very safe — that’s why it’s allowed.
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Re: Baltimore's Key Bridge struck by cargo ship, collapses
#183Earlier quoted context omitted.
Most bridges nowadays (say last century) depend on a careful balance of forces that are transferred through a chain of members in tension and compression. When any piece in the chain of those forces breaks, the entire structure loses ability to transfer forces and breaks. This arrangement is what allows us to build these structures in the first place. There is careful calculations of forces and risks and allowance fo…
“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.” And in practice only bridges that "barely" stand are economically viable
> only bridges that "barely" stand are economically viable
That really depends on what is counted as part of the economy and who is doing the valuing.
Re: Baltimore's Key Bridge struck by cargo ship, collapses
#184Earlier quoted context omitted.
It's no surprise that the entire bridge collapses after a pylon collapses. What surprises me is that the pylon collapses. I'd expect those to be extremely solid, with tons of padding. But with ships getting bigger and bigger, I guess there's a limit to what you can account for.
Ships are hundreds of thousands of tons in weight and the momentum acts as a force multiplier. Plus it hit the pylon dead center, which is the worst case scenario. It’s not terribly surprising. I think there’s also an underlying expectation that any competent ship captain would at least be able to see that they’re on a collision course with the pylon well ahead of time and be able to compensate. Which obviously didn’…
There is another video where we can see two power outage occurred. Ship was uncontrollable but with enormous amount of inertia.
I'm sure captain tried to do anything he can to avoid collision.
Re: Baltimore's Key Bridge struck by cargo ship, collapses
#185Earlier quoted context omitted.
from what I can tell it didn't look like vehicles, it looked like road maintenance, so people outside and maybe a vehicle. only difference is not trapped in vehicle, everything else still dire
There's a slight benefit that a road crew will be dressed for nighttime outside weather, with reflective clothing, are all adults, and probably have some level of physical fitness.
If you're going to be dropped into water, heavy clothing is probably very much not what you want.
Re: Baltimore's Key Bridge struck by cargo ship, collapses
#186Somehow 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…
There is this often in HN featured article about bridge engineer analysing bridge collapses in film [1]. It’s about suspension bridges though but the takeaway for me was that when they go they go completely.
[1] https://hackaday.com/2015/11/18/suspension-bridges-of-disbel...
Re: Baltimore's Key Bridge struck by cargo ship, collapses
#187Earlier quoted context omitted.
Most bridges nowadays (say last century) depend on a careful balance of forces that are transferred through a chain of members in tension and compression. When any piece in the chain of those forces breaks, the entire structure loses ability to transfer forces and breaks. This arrangement is what allows us to build these structures in the first place. There is careful calculations of forces and risks and allowance fo…
On a long enough timeline we all get rammed by a container ship. I would be interested to know some calculations with factors like: expected bridge lifetime, chance of being rammed per year, cost of making supports strong enough plus an extra safety margin to survive maximum ramming force, cost of having major commercial shipping route unusable for an extended period.
Bridges only last for roughly 50 years. Considering such collisions are rare enough to make the news as a memorable event you can workout for yourself that the odds are quite low over a bridges lifespan.
They are designed to withstand smaller boat impacts because they occur relatively frequently, but cost vs benefit on rare events that are difficult to mitigate is quite different.
Re: Baltimore's Key Bridge struck by cargo ship, collapses
#188Earlier quoted context omitted.
This situation is terrible, but to your specific question: Anyone can build a bridge, but it takes an engineer to barely make it stand.
I like this quote. We have a medieval bridge near to our house (1000 years old perhaps), it's incredibly solidly built, but could you call it well-engineered? It's a subtle distinction that I don't think many in the digital realm quite grasp either i.e. far too many over-engineered technical solutions for features and products that aren't even desired
> could you call it well-engineered?
What is well engineered depends on the goals and the limitations of the state of the art at the time. I would say that a thousand year old bridge might count as well engineered if the goal was a bridge that had a low total lifetime cost.
Re: Baltimore's Key Bridge struck by cargo ship, collapses
#189Earlier 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…
> But I think the true definition of engineering has to encompass a level of efficiency through design, calculation and rationalization.
The 1000 year medieval bridge we're talking about could have been an efficient design for its time.
Re: Baltimore's Key Bridge struck by cargo ship, collapses
#190You can look back on the livestream here to see the collision and collapse. https://www.youtube.com/watch?v=83a7h3kkgPg
Clip here, beginning at 1m23s, shows a (sped-up) edit of the ship approaching the bridge, with lights going out, on, and out again immediately prior to impact: https://yewtu.be/watch?v=Cs6PrRiIHEw&t=1m23s >
Curious, is there a specific reason you put links between ?