6 ms·

What caused Seattle crane to collapse?

49 points by curtis 7y ago

OldManAndTheCpp 7y ago
They took the pins out! https://youtu.be/cexN2-T6dxY https://youtu.be/cexN2-T6dxY
- grenoire 7y ago
  AvE strikes again.
- rfrey 7y ago
  AvE did two videos on the collapse, both very good. The comments are excellent, and worth skimming even if you’re generally allergic to YouTube comments. There are explanations from several ironworkers who actually erect and dismantle cranes, as well as from managers and foremen.
michaelt 7y ago
sometimes they’re loosened all the way to “finger tight,” sometimes a few pins are removed ahead of time [...] “It saves time, which equals money.” I'd have thought the time it takes the supporting crane to lower the top section to the ground would have been greater than the time it takes to remove eight bolts. After all, presumably the guys doing this for a living have the best tools available. Does anyone know why removing the bolts is so slow? Or is the supporting crane actually really fast?
- dmurray 7y ago
  My first guess was that you have to climb back down to the ground between each section being removed, for safety reasons (don't get hit by a swinging section of crane). But in that case you'd still have to climb to remove the last two bolts, so it doesn't really save anything.
- steve_g 7y ago
  I would guess it saves crane time for the supporting crane. If the bolts are loosened before the supporting crane begins operating, the total start to finish crane time can be less. Of course, the tower's resistance to overturning moment is reduced during that time - to what appears to be fatal results in this case. Not worth it.
- londons_explore 7y ago
  It might be along the same lines as your mom telling you to do the washing up now rather than later when you need the dishes. It's the same effort now and later, but putting it off makes you look lazy. Someone was probably keen to impress the boss and say "Look, we've removed all the pins so that cranes ready to come down. Nothing else to do now! 2 days ahead of schedule!".
- moring 7y ago
  Thinking about it, they need to remove eight bolts per section, then the section itself, then eight bolts for the next section, and so on. I could have expected them to save time by removing the bolts of the second top section in parallel to the supporting crane removing the top section, but removing the bolts of all sections only makes sense when the supporting crane is actually faster than the bolt-removing guy/team. Something else might be going on -- maybe they did not want the workers who were removing the bolts to wait for the supporting crane and sent them home to save on wages or gave them other work to do.
kieranmaine 7y ago
Seems like a good example of the Normalization of Deviance. Instantly made me think of this post form the other day https://news.ycombinator.com/item?id=19770562 https://news.ycombinator.com/item?id=19770562.
- YUMad 7y ago
  Society has stopped being self-regulating. It's the same result as zero-tolerance for violence school policies, just on a larger scale.
  - specialist 7y ago
    I often think that we're missing feedback loops, so learning opportunities are wasted.
londons_explore 7y ago
This article confuses bolts and pins... Removing the bolts doesn't really have an impact on strength. A lack of a bolt can cause wear on a pin as the structure flexes, but typically unless you're leaving it for years that wouldn't be an issue. You can inspect the wear the next time you use the pin. Removing pins weakens the structure substantially. However when the crane isn't in use, it doesn't need anywhere near all of it's strength, so removing one of two pins is fine. I would guess in this case, they removed 2 of 2 pins, leaving gravity the only thing holding everything in place, which is plain stupid.
- dmurray 7y ago
  Can you explain the difference some more? I think of a bolt as a pin with threads, that gets secured with a nut on the other end. A pin has no thread and gets secured by putting another piece through a hole in the end of it. So they have different failure modes (a bolt can get its thread stripped, or vibrate the nut off) but otherwise can be used interchangeably. What's the structural difference you are referring to?
  - TheSpiceIsLife 7y ago
    Bolts are (generally?) intended to apply force between two surfaces and not themselves act as shear resistance. Whereas a pin is (generally?) entirely a shear-force resistance component.
    - dreamcompiler 7y ago
      Right. Bolts are usually weak in shear but strong in tension.Their job is to create high friction between two pieces; that friction joins the two pieces as one.
  - tyingq 7y ago
    See this diagram: https://static.seattletimes.com/wp-content/uploads/2019/05/crane-pins-WEB-1020x602.jpg https://static.seattletimes.com/wp-content/uploads/2019/05/c... I believe the metal sleeves that the bolts go into are the pins. Edit: I probably shouldn't have said "sleeves". That has more than one meaning in this context. I'm talking about hollow pins, secured by bolts when I say "sleeves".
nn3 7y ago
This might be a stupid question, but how is the assisting crane finally disassembled? Is it a different type that doesn't need disassembling in the same way?
- lemcoe9 7y ago
  https://www.youtube.com/watch?v=rLcxROazqy8 https://www.youtube.com/watch?v=rLcxROazqy8 This is Liebherr LG 1750 which is a "mobile crawler crane" that is completely self-propelled and self-assembling.
- cmsmith 7y ago
  Yes, the assisting crane is a mobile crane where the boom pivots up and down about the base. Some have booms that need to be disassembled piece-by-piece, so you just pivot it down until the top is resting on a flatbed trailer, then unbolt it. These mobile cranes can reach just as high as tower cranes, but can't carry as much, can't reach out over the tops of buildings, and take up more room on the ground. Hence the need for tower cranes.
  - tomatotomato37 7y ago
    Another interesting advatange of tower cranes is that they can grow/shrink themselves by using a special jig; that's how they're able to negotiate 200 story skyscrapers. That jigs tends to be too convulted to use for smaller projects, in which case they use a mobile crane as seen here.
    - jjtheblunt 7y ago
      200 story skyscrapers? In some other universe?
- jacurtis 7y ago
  This was my same thought. If it takes a crane to build another crane, then why not use the first crane to begin with?
  - 7y ago
emilecantin 7y ago
AvE on youtube came to the same conclusion 2 weeks ago: https://www.youtube.com/watch?v=cexN2-T6dxY https://www.youtube.com/watch?v=cexN2-T6dxY And a follow-up after new pictures became available further confirms this: https://www.youtube.com/watch?v=7Wo7J_buZUE https://www.youtube.com/watch?v=7Wo7J_buZUE The article makes it seem like it's a common practice in the industry. Pretty scary! I don't really understand how it saves time, though... I'd think the bottleneck is the heavy-lift crane, isn't it?
- a2tech 7y ago
  In the AvE comments there's a lot of people claiming that this is NOT a common practice--because its incredibly dangerous. It just takes a gust of wind when those pins are out to cause massive damage.
  - kurthr 7y ago
    Except now somebody's boss is going to site this article to show it's common practice (I'm only partially kidding) or only remember the removing pins saving time part. I'm reminded of the LA TV news shorts reminding people not to modify their lighters to continuously spew flame and throw them out the window on the freeway. The alignment of stupidity and (anti)social incentives to risk other people's lives is a dangeous thing. Antivax rallies come to mind.
- HissingMachine 7y ago
  It's not hard to imagine that the practice is common. I know I'm cutting corners and don't know anything about construction, but if you make a little mental game out of it. If you have 20 men on site, dismantling crane probably shuts down most of the work on site, so you have to send most of the 20 men home during dismantling. You hire an outside contractor to dismantle the crane, so you probably want it to only take a day to cut costs on outsourcing and worker leave, you bring the dismantling crew in the morning to remove the pins and the lift the pieces off on the afternoon. There are thousands of cranes all over the world and there are probably dozens erected and dismantled daily. If we only have a disaster every couple of years, out of the hundreds of operations, that's when the practice get's exposed, it's like lottery but you win every time if you don't happen to hold the winning ticket. Truth of it is, many of us roll the dice with those odds.
annadane 7y ago
Neurotic fights with his brother Niles and father Martin

49 points by curtis 7y ago

OldManAndTheCpp 7y ago

They took the pins out! https://youtu.be/cexN2-T6dxY https://youtu.be/cexN2-T6dxY

grenoire 7y ago
AvE strikes again.
rfrey 7y ago
AvE did two videos on the collapse, both very good. The comments are excellent, and worth skimming even if you’re generally allergic to YouTube comments. There are explanations from several ironworkers who actually erect and dismantle cranes, as well as from managers and foremen.

michaelt 7y ago

sometimes they’re loosened all the way to “finger tight,” sometimes a few pins are removed ahead of time [...] “It saves time, which equals money.” I'd have thought the time it takes the supporting crane to lower the top section to the ground would have been greater than the time it takes to remove eight bolts. After all, presumably the guys doing this for a living have the best tools available. Does anyone know why removing the bolts is so slow? Or is the supporting crane actually really fast?

dmurray 7y ago
My first guess was that you have to climb back down to the ground between each section being removed, for safety reasons (don't get hit by a swinging section of crane). But in that case you'd still have to climb to remove the last two bolts, so it doesn't really save anything.
steve_g 7y ago
I would guess it saves crane time for the supporting crane. If the bolts are loosened before the supporting crane begins operating, the total start to finish crane time can be less. Of course, the tower's resistance to overturning moment is reduced during that time - to what appears to be fatal results in this case. Not worth it.
londons_explore 7y ago
It might be along the same lines as your mom telling you to do the washing up now rather than later when you need the dishes. It's the same effort now and later, but putting it off makes you look lazy. Someone was probably keen to impress the boss and say "Look, we've removed all the pins so that cranes ready to come down. Nothing else to do now! 2 days ahead of schedule!".
moring 7y ago
Thinking about it, they need to remove eight bolts per section, then the section itself, then eight bolts for the next section, and so on. I could have expected them to save time by removing the bolts of the second top section in parallel to the supporting crane removing the top section, but removing the bolts of all sections only makes sense when the supporting crane is actually faster than the bolt-removing guy/team. Something else might be going on -- maybe they did not want the workers who were removing the bolts to wait for the supporting crane and sent them home to save on wages or gave them other work to do.

kieranmaine 7y ago

Seems like a good example of the Normalization of Deviance. Instantly made me think of this post form the other day https://news.ycombinator.com/item?id=19770562 https://news.ycombinator.com/item?id=19770562.

YUMad 7y ago
Society has stopped being self-regulating. It's the same result as zero-tolerance for violence school policies, just on a larger scale.
- specialist 7y ago
  I often think that we're missing feedback loops, so learning opportunities are wasted.

londons_explore 7y ago

This article confuses bolts and pins... Removing the bolts doesn't really have an impact on strength. A lack of a bolt can cause wear on a pin as the structure flexes, but typically unless you're leaving it for years that wouldn't be an issue. You can inspect the wear the next time you use the pin. Removing pins weakens the structure substantially. However when the crane isn't in use, it doesn't need anywhere near all of it's strength, so removing one of two pins is fine. I would guess in this case, they removed 2 of 2 pins, leaving gravity the only thing holding everything in place, which is plain stupid.

dmurray 7y ago
Can you explain the difference some more? I think of a bolt as a pin with threads, that gets secured with a nut on the other end. A pin has no thread and gets secured by putting another piece through a hole in the end of it. So they have different failure modes (a bolt can get its thread stripped, or vibrate the nut off) but otherwise can be used interchangeably. What's the structural difference you are referring to?
- TheSpiceIsLife 7y ago
  Bolts are (generally?) intended to apply force between two surfaces and not themselves act as shear resistance. Whereas a pin is (generally?) entirely a shear-force resistance component.
  - dreamcompiler 7y ago
    Right. Bolts are usually weak in shear but strong in tension.Their job is to create high friction between two pieces; that friction joins the two pieces as one.
- tyingq 7y ago
  See this diagram: https://static.seattletimes.com/wp-content/uploads/2019/05/crane-pins-WEB-1020x602.jpg https://static.seattletimes.com/wp-content/uploads/2019/05/c... I believe the metal sleeves that the bolts go into are the pins. Edit: I probably shouldn't have said "sleeves". That has more than one meaning in this context. I'm talking about hollow pins, secured by bolts when I say "sleeves".

nn3 7y ago

This might be a stupid question, but how is the assisting crane finally disassembled? Is it a different type that doesn't need disassembling in the same way?

lemcoe9 7y ago
https://www.youtube.com/watch?v=rLcxROazqy8 https://www.youtube.com/watch?v=rLcxROazqy8 This is Liebherr LG 1750 which is a "mobile crawler crane" that is completely self-propelled and self-assembling.
cmsmith 7y ago
Yes, the assisting crane is a mobile crane where the boom pivots up and down about the base. Some have booms that need to be disassembled piece-by-piece, so you just pivot it down until the top is resting on a flatbed trailer, then unbolt it. These mobile cranes can reach just as high as tower cranes, but can't carry as much, can't reach out over the tops of buildings, and take up more room on the ground. Hence the need for tower cranes.
- tomatotomato37 7y ago
  Another interesting advatange of tower cranes is that they can grow/shrink themselves by using a special jig; that's how they're able to negotiate 200 story skyscrapers. That jigs tends to be too convulted to use for smaller projects, in which case they use a mobile crane as seen here.
  - jjtheblunt 7y ago
    200 story skyscrapers? In some other universe?
jacurtis 7y ago
This was my same thought. If it takes a crane to build another crane, then why not use the first crane to begin with?
- 7y ago

emilecantin 7y ago

AvE on youtube came to the same conclusion 2 weeks ago: https://www.youtube.com/watch?v=cexN2-T6dxY https://www.youtube.com/watch?v=cexN2-T6dxY And a follow-up after new pictures became available further confirms this: https://www.youtube.com/watch?v=7Wo7J_buZUE https://www.youtube.com/watch?v=7Wo7J_buZUE The article makes it seem like it's a common practice in the industry. Pretty scary! I don't really understand how it saves time, though... I'd think the bottleneck is the heavy-lift crane, isn't it?

a2tech 7y ago
In the AvE comments there's a lot of people claiming that this is NOT a common practice--because its incredibly dangerous. It just takes a gust of wind when those pins are out to cause massive damage.
- kurthr 7y ago
  Except now somebody's boss is going to site this article to show it's common practice (I'm only partially kidding) or only remember the removing pins saving time part. I'm reminded of the LA TV news shorts reminding people not to modify their lighters to continuously spew flame and throw them out the window on the freeway. The alignment of stupidity and (anti)social incentives to risk other people's lives is a dangeous thing. Antivax rallies come to mind.
HissingMachine 7y ago
It's not hard to imagine that the practice is common. I know I'm cutting corners and don't know anything about construction, but if you make a little mental game out of it. If you have 20 men on site, dismantling crane probably shuts down most of the work on site, so you have to send most of the 20 men home during dismantling. You hire an outside contractor to dismantle the crane, so you probably want it to only take a day to cut costs on outsourcing and worker leave, you bring the dismantling crew in the morning to remove the pins and the lift the pieces off on the afternoon. There are thousands of cranes all over the world and there are probably dozens erected and dismantled daily. If we only have a disaster every couple of years, out of the hundreds of operations, that's when the practice get's exposed, it's like lottery but you win every time if you don't happen to hold the winning ticket. Truth of it is, many of us roll the dice with those odds.

annadane 7y ago

Neurotic fights with his brother Niles and father Martin