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So if they knew there is no money to even maintain it and this collapse was a likely outcome why not lower the platform in advance before any cable breaks? Just

So if they knew there is no money to even maintain it and this collapse was a likely outcome why not lower the platform in advance before any cable breaks? Just from a safety perspective omitting this seems to be somewhat negligent, no?

AlgorithmicTime 6y ago
Lower it to where? It would crush the reflective dish.
Gene5ive 6y ago
They were about to. I'm pretty sure they were using the drone to get ahead of that problem. Seems like it happened to fast.
latchkey 6y ago
How do you safely lower a platform that might break at any point?
masklinn 6y ago
I'm not sure it was possible, the cables were likely anchored (frayed then sunk in concrete), it would have required setting up a mobile anchor, cutting the cable from the anchor, adding lengths of cables somehow, and unspooling those extra lengths. It's already not done for suspension bridges[0], I don't think it could be done here. And the risk would obviously have been gigantic as two cables had already snapped in the same place, so the remaining cables would be under insane and completely out of spec tensions, meaning they could fail at any point during the tentative transfer work. [0] you either splay open the main cables and replace strands, or you need to jack the entire bridge from below to take down and replace the main cables at once
- robocat 6y ago
  Quick google: Presently, cable replacement designs are being developed for three suspension bridges in the United States. All three are important river crossings at or near a major metropolitan area and must remain open to traffic during construction. These cable replacement designs will need to overcome myriad difficulties, including cable support at the existing tower tops and placement of new anchorages within restricted available spaces. Alternatives will include placing the new cables above or adjacent to the existing ones. The construction procedures and load transfer sequencing is a critical part of the design. The new cables will need to be erected in their free position and will undergo substantial deformations as the load is transferred to them. Additionally, the existing cables and towers will undergo their own deformations, as will the bridge superstructure as it is released from the old and supported by the new suspension system. The work will require extensible hangers to accomplish the load transfer, and all operations must be coordinated to limit changes in the roadway geometry and stresses in the superstructure, towers and suspension components.
Tuna-Fish 6y ago
As it existed, it didn't have any of the equipment needed to lower it. It was raised to it's position with temporary equipment, then the cables that held it up were fixed in place, and then the temporary equipment was removed. So to lower it, they'd have had to do a lot work adding stuff near the cables. Which they already knew to be a lot weaker than they were supposed to be, and of which two had already failed. That would have been the really negligent thing to do, instead of just removing all people from near the dish which was done.
nomel 6y ago
> Just from a safety perspective There is no safety perspective if there is nobody there to get hurt. It has been evacuated for a long time now. Putting people anywhere near it would create the safety concern.
pkaye 6y ago
According to the Wikipedia entry... > The NSF made the announcement on November 19, 2020 that they would decommission Arecibo over the following few weeks after determining the safest route to do so with a safety exclusion zone immediately put in place.
jcranmer 6y ago
There is no way to lower the platform safely. The cables are anchored to the saddle block you see in the drone footage. The closest you can get to a safe lowering would be to sever all the anchor points simultaneously so that the platform falls vertically, rather than having a rotational component due to differing total tension forces. And even then, I don't see how that can be done particularly safely, given that any human in proximity to any of the towers at the time of premature collapse would be dead. Just to reiterate: any person working on the support tower platform would have been dead. If not from the cable snapping (you can see how much damage it does to the remaining cables!), then from the support tower itself toppling over a few seconds later.
deleted 6y ago
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AlgorithmicTime 6y ago

Lower it to where? It would crush the reflective dish.

Gene5ive 6y ago

They were about to. I'm pretty sure they were using the drone to get ahead of that problem. Seems like it happened to fast.

latchkey 6y ago

How do you safely lower a platform that might break at any point?

masklinn 6y ago

I'm not sure it was possible, the cables were likely anchored (frayed then sunk in concrete), it would have required setting up a mobile anchor, cutting the cable from the anchor, adding lengths of cables somehow, and unspooling those extra lengths. It's already not done for suspension bridges[0], I don't think it could be done here. And the risk would obviously have been gigantic as two cables had already snapped in the same place, so the remaining cables would be under insane and completely out of spec tensions, meaning they could fail at any point during the tentative transfer work. [0] you either splay open the main cables and replace strands, or you need to jack the entire bridge from below to take down and replace the main cables at once

robocat 6y ago
Quick google: Presently, cable replacement designs are being developed for three suspension bridges in the United States. All three are important river crossings at or near a major metropolitan area and must remain open to traffic during construction. These cable replacement designs will need to overcome myriad difficulties, including cable support at the existing tower tops and placement of new anchorages within restricted available spaces. Alternatives will include placing the new cables above or adjacent to the existing ones. The construction procedures and load transfer sequencing is a critical part of the design. The new cables will need to be erected in their free position and will undergo substantial deformations as the load is transferred to them. Additionally, the existing cables and towers will undergo their own deformations, as will the bridge superstructure as it is released from the old and supported by the new suspension system. The work will require extensible hangers to accomplish the load transfer, and all operations must be coordinated to limit changes in the roadway geometry and stresses in the superstructure, towers and suspension components.

Tuna-Fish 6y ago

As it existed, it didn't have any of the equipment needed to lower it. It was raised to it's position with temporary equipment, then the cables that held it up were fixed in place, and then the temporary equipment was removed. So to lower it, they'd have had to do a lot work adding stuff near the cables. Which they already knew to be a lot weaker than they were supposed to be, and of which two had already failed. That would have been the really negligent thing to do, instead of just removing all people from near the dish which was done.

nomel 6y ago

> Just from a safety perspective There is no safety perspective if there is nobody there to get hurt. It has been evacuated for a long time now. Putting people anywhere near it would create the safety concern.

pkaye 6y ago

According to the Wikipedia entry... > The NSF made the announcement on November 19, 2020 that they would decommission Arecibo over the following few weeks after determining the safest route to do so with a safety exclusion zone immediately put in place.

jcranmer 6y ago

There is no way to lower the platform safely. The cables are anchored to the saddle block you see in the drone footage. The closest you can get to a safe lowering would be to sever all the anchor points simultaneously so that the platform falls vertically, rather than having a rotational component due to differing total tension forces. And even then, I don't see how that can be done particularly safely, given that any human in proximity to any of the towers at the time of premature collapse would be dead. Just to reiterate: any person working on the support tower platform would have been dead. If not from the cable snapping (you can see how much damage it does to the remaining cables!), then from the support tower itself toppling over a few seconds later.

deleted 6y ago

[deleted]