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Tae Bo Workout Sent Skyscraper Shaking
MiniMike writes "According to CNN: 'Seventeen people performing a vigorous Tae Bo workout caused tremors that forced the evacuation of a South Korean skyscraper earlier this month, the building's owners say.
Scientists recreated the event in the 12th floor gym, according to a report in the Korea Times.' I don't know which is scarier, that they made such a flimsy skyscraper, or the sight of 17 scientists doing a Tae Bo workout. Hopefully they're better at it than the scientists I've seen in the gym."
Which bridge? The Tacoma Narrows Bridge, that shook itself apart, is one famous example, but it's not the only one. The Millennium Bridge in London had a similar problem. If people walked across it at a normal walking pace, their footsteps were at the bridge's resonant frequency. Worse, when a bridge starts to resonate like that, people naturally start walking in sync with the vibrations, making it worse. It cost £5m to fix - over 25% of the original construction cost.
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The article concerns a workout which happened to hit the resonant frequency of the structure, which was properly designed. The failure you linked to had to do with criminal negligence by the owners ignoring repeated engineering and construction firms who refused to accept design changes driven by greed (and were fired for it), completely repurposed building usage leading to gross overloading of the structure's strength, and then completely incompetent handling of obvious signs of structural failure (failure to immediately evacuate the building.) For fuck's sakes, they removed columns for escalators, then cut into the remaining columns, then ADDED A STORY WITH POURED CONCRETE FLOORS *and* an air conditioning unit the building wasn't designed for. And then when the building started to fail, they just blocked off areas to hide it from customers because they didn't want to lose sales revenue.
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Too bad you learned something wrong.
Galloping Gertie was brought down by aeroelastic flutter, aka forced resonance. Aeroelastic flutter is more specific, but not a correction.
Galloping Gertie was visibly resonant in its second harmonic, in torsion. Structures have more then one resonance frequency. All those frequencies have harmonics.
John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'
OP here. The end of my submission, where I include that IAAS (scientist), was cut off, so I would like to state that I wasn't trying to convey a "where (sic) better than they are" attitude. I could have stated my intent with the last surviving sentence more clearly. While many scientists I see in the gym are in great shape, some of them are in quite poor shape and uncoordinated. The ones at that end of the spectrum are usually in the beginner group exercise classes. It is that group I was trying to reference in the post. The last sentence should have read 'some of the scientists'. Hope this clears it up.
So, I'm no expert here, but is it REALLY possible to design a building which does not resonate at any frequency?
You need a way to dump the energy into some other form, there are multiple ways of doing that, I linked to one in an earlier post. You don't have to dump all of the energy, just enough to prevent it from becoming structurally dangerous within certain margins. I think it is entirely reasonable to expect a building to avoid shaking 19 floors because about 10 people are jumping around. It isn't like they are putting a whole lot of energy into the structure to begin with.
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