
What caused Seattle crane to collapse? - curtis
https://www.seattletimes.com/seattle-news/what-caused-seattle-crane-to-collapse-experts-say-a-common-practice-is-likely-cause/
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emilecantin
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
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
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.

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kieranmaine
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
Society has stopped being self-regulating. It's the same result as zero-
tolerance for violence school policies, just on a larger scale.

~~~
specialist
I often think that we're missing feedback loops, so learning opportunities are
wasted.

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OldManAndTheCpp
They took the pins out!

[https://youtu.be/cexN2-T6dxY](https://youtu.be/cexN2-T6dxY)

~~~
rfrey
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.

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londons_explore
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
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
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
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.

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nn3
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?

~~~
cmsmith
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
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
200 story skyscrapers? In some other universe?

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michaelt

      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?

~~~
moring
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.

