5 ms·

>>But I guess I thought that maybe there was... typically some kind of earthen buffer around the pillar to prevent such an impact? It does look reasonable to h

by kamaal 3y ago

>>But I guess I thought that maybe there was... typically some kind of earthen buffer around the pillar to prevent such an impact? It does look reasonable to have such a buffer. But any preventive measure will have limits as what and how serious an impact it can deal with. In this case the ship this massive is something that is carrying ridiculous inertia, and its highly unlikely even a buffer could stop such an impact. I think at some point you are better off solving these issues with more regulation(smaller ships)? Instead of treating this as a engineering problem.

unsupp0rted 3y ago
It wouldn't take as much of a buffer to redirect the ship at an angle away from the pillar, would it?
- kergonath 3y ago
  I think this would be even harder. Whilst the ship has a lot of kinetic energy that needs to get dissipated, it also has a huge momentum that needs to be partly overcome to redirect it. You’d also need a material with enough structural strength to turn the ship. Materials that can crumple or deform (like huge concrete blocks or earthworks) are great at dissipating energy, but they aren’t great at deflecting things.
mannykannot 3y ago
> But any preventive measure will have limits as what and how serious an impact it can deal with. The recent grounding of a large container ship in Baltimore's harbor channel demonstrates that a sufficiently massive berm will stop any ship. What's needed is the will to do something about low-probability but catastrophic events (though large-ship collisions, groundings and fortuitously harmless steering failures are frequent enough that this should not have been dismissed as a low-probability event.) https://www.cnn.com/2022/03/16/business/evergreen-container-ship-grounded/index.html https://www.cnn.com/2022/03/16/business/evergreen-container-... In this case, the nearby towers supporting transmission lines across the channel seem to be better-protected against ship collisions than the piers of the bridge. https://images.app.goo.gl/J6vTeDW5xjysbdjr9 https://images.app.goo.gl/J6vTeDW5xjysbdjr9
- rkagerer 3y ago
  What's needed is the will to do something about low-probability but catastrophic events In general I share your sentiment society could do more to insure itself against lower-probability catastrophes. But overbuilding every bridge would probably cost more than rebuilding the occasional one that's taken out when an unusual event like this occurs. Maybe in a different environment that would make sense, like a warzone (although I think even then there's more tendency to rely on redundant infrastructure and mobile, power-at-a-point defense).
- deleted 3y ago
  [deleted]
- throwaway48476 3y ago
  The "berm" in this case happens to be the seabed of the earth. There's nothing bigger.
  - mannykannot 3y ago
    Of course - but it doesn't take all of it...
- bmelton 3y ago
  Starting from xoa's calculations above, assuming you can pack a berm with well-compacted soil enough that it can absorb 1,000 joules per cubic meter, you'd need a buffer of something like 10 meters surrounding each piling with 3 meters of depth to keep it safe from this kind of impact. That's 10 meters in every direction from the center of the support -- let's assume the support has a thickness of 0 meters for the sake of the math, and acknowledging that the gaps between structural supports on the bridge is approximately 30 meters -- the only way to protect it with earth is to make the bridge impassable by water. Of course, this would protect it from ship strikes.
  - SiempreViernes 3y ago
    You needn't stop the ship completely with the berm: just taking up enough energy that the bridge lives for 20 minutes after the impact would be useful.
deleted 3y ago
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by kamaal 3y ago

unsupp0rted 3y ago

It wouldn't take as much of a buffer to redirect the ship at an angle away from the pillar, would it?

kergonath 3y ago
I think this would be even harder. Whilst the ship has a lot of kinetic energy that needs to get dissipated, it also has a huge momentum that needs to be partly overcome to redirect it. You’d also need a material with enough structural strength to turn the ship. Materials that can crumple or deform (like huge concrete blocks or earthworks) are great at dissipating energy, but they aren’t great at deflecting things.

mannykannot 3y ago

> But any preventive measure will have limits as what and how serious an impact it can deal with. The recent grounding of a large container ship in Baltimore's harbor channel demonstrates that a sufficiently massive berm will stop any ship. What's needed is the will to do something about low-probability but catastrophic events (though large-ship collisions, groundings and fortuitously harmless steering failures are frequent enough that this should not have been dismissed as a low-probability event.) https://www.cnn.com/2022/03/16/business/evergreen-container-ship-grounded/index.html https://www.cnn.com/2022/03/16/business/evergreen-container-... In this case, the nearby towers supporting transmission lines across the channel seem to be better-protected against ship collisions than the piers of the bridge. https://images.app.goo.gl/J6vTeDW5xjysbdjr9 https://images.app.goo.gl/J6vTeDW5xjysbdjr9

rkagerer 3y ago
What's needed is the will to do something about low-probability but catastrophic events In general I share your sentiment society could do more to insure itself against lower-probability catastrophes. But overbuilding every bridge would probably cost more than rebuilding the occasional one that's taken out when an unusual event like this occurs. Maybe in a different environment that would make sense, like a warzone (although I think even then there's more tendency to rely on redundant infrastructure and mobile, power-at-a-point defense).
deleted 3y ago
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throwaway48476 3y ago
The "berm" in this case happens to be the seabed of the earth. There's nothing bigger.
- mannykannot 3y ago
  Of course - but it doesn't take all of it...
bmelton 3y ago
Starting from xoa's calculations above, assuming you can pack a berm with well-compacted soil enough that it can absorb 1,000 joules per cubic meter, you'd need a buffer of something like 10 meters surrounding each piling with 3 meters of depth to keep it safe from this kind of impact. That's 10 meters in every direction from the center of the support -- let's assume the support has a thickness of 0 meters for the sake of the math, and acknowledging that the gaps between structural supports on the bridge is approximately 30 meters -- the only way to protect it with earth is to make the bridge impassable by water. Of course, this would protect it from ship strikes.
- SiempreViernes 3y ago
  You needn't stop the ship completely with the berm: just taking up enough energy that the bridge lives for 20 minutes after the impact would be useful.

deleted 3y ago

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