Loose Change: Astrotower
July 8, 2013 9:42 PM   Subscribe

The Coney Island Luna Park Astrotower was dismantled this July 4th. The reason given was because weight was removed from the top of the tower it began abnormally swaying, so it had to come down. The swaying was reported by an unidentified tourist. This seems fishy to me, especially the claim that a lighter, less top heavy structure would be less stable. Was there an actual safety issue, or was it more likely that there was some kind of conspiracy to bring the tower down?
posted by Sophont to Science & Nature (5 answers total) 1 user marked this as a favorite
There's video of the tower here. It looks... not great.
posted by fox problems at 10:02 PM on July 8, 2013 [1 favorite]

I don't know anything about the Astro tower specifically.

FDNY calls structure "unstable"
Luna Park shut down 4 July
Coney Island's Astrotower Is Swaying, Scaring
Coney Island's Astro Tower called unstable, causes shutdown - "The New York City Buildings Department called emergency officials to the amusement park after onlookers reported the 270-foot-tall, 50-year-old tower was swaying, according to a spokeswoman at the Office of Emergency Management"
Coney Island icon Astro Tower in peril as NYC set to dismantle swaying spire

So: people report Astro Tower swaying, which is apparently not unusual. But the Astro Tower has had the gondola and counterweights removed, which changes the mass, moment and harmonics of the tower.

Removing material can change the periodicity of the tower's swaying, which may have unintended side effects. It's not just a matter of "less top heavy structure would be less stable." This also assumes that portions of the tower were removed correctly.

Old modified structure is old, modified.
posted by the man of twists and turns at 10:04 PM on July 8, 2013 [1 favorite]

Sure looks like a safety issue to me, something that you don't need an engineering degree to sense. I can't imagine what conspiracy is in place here -- it's not like it occupied a huge slice of land that is ripe for redevelopment into condos or something.

I think I would focus on the positive that the parachute jump is getting improvements and the Cyclone (in some opinions the best rollercoaster there ever was) continues to operate. Not all of the old rides were ever safe by 21st century standards and probably could not be made safe. There's some gentrification and redevelopment taking place in the area but that would happen with investment, and while I appreciate the point of view of the nostalgia for its funkier, seedier era, keeping it that way (and I was there when there was broken glass and needles everywhere) was a recipe for its demise.
posted by dhartung at 1:38 AM on July 9, 2013

Structures can have resonant frequencies that are damped out by a large mass. Remove the mass and the resonance appears.

Not sure if this is what happened in this case, but it is a physical possibility.
posted by gjc at 6:38 AM on July 9, 2013

the man of twists and turns has it. A lighter, less top heavy structure will have a different resonant frequency, and if that frequency is close to forcing frequencies from wind loads, passenger traffic, tae bo, etc., hilarity will not ensue.

Some of the wind turbines I've built have ballast tanks at tower top to avoid resonance. Some even have pendulums in the tanks to act as dampers (sometimes resulting in a timpani-like bonging noise after a hard stop). Avoiding resonance is incredibly important for structural safety.
posted by scruss at 7:05 AM on July 9, 2013

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