Shaking apartment

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Shaking apartment

Postby Vellyr » Tue Jul 05, 2011 3:06 am UTC

So I live about 100 yards from some train tracks on the third floor, and every time a train goes by I feel the apartment shake. The thing is, I don't feel anything when I stand right next to the tracks, only in my apartment. Is there some kind of phenomenon that could explain this, or is it all in my head?

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Re: Shaking apartment

Postby 314man » Tue Jul 05, 2011 3:48 am UTC

I think it's just that the apartment itself shakes (much more than the solid ground), so you will feel the ground beneath your feet shake more when you're in your apartment.
Kind of like if you try to stay balanced on a carpet while someone is moving it randomly; it's easier to balance standing on the shaky carpet than standing on top of a chair that is on the carpet

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Re: Shaking apartment

Postby mmmcannibalism » Tue Jul 05, 2011 3:51 am UTC

being on the 3rd floor might be causing a sort of swaying; like how a golf club bends more at the top then at the bottom when swung.
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Re: Shaking apartment

Postby Izawwlgood » Tue Jul 05, 2011 4:33 am UTC

Resonance. Everything is going to explode.
... with gigantic melancholies and gigantic mirth, to tread the jeweled thrones of the Earth under his sandalled feet.

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Re: Shaking apartment

Postby vega12 » Fri Jul 08, 2011 4:11 pm UTC

Yeah, it's just due to being high above the ground as mentioned. For example, I live on a 12th floor of an apartment in Tokyo and can sometimes feel earthquakes that outside are almost imperceptible.

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Re: Shaking apartment

Postby gorcee » Fri Jul 08, 2011 5:13 pm UTC

The reason is has to do with being "on high ground" has to do with mechanical effects.

If you're standing next to the tracks, you don't feel the ground sway because there fewer components between it and you -- namely just your knees and ankles. But, if you're in a building a few stories up, the effect feels magnified.

The vibrations are essentially forces being transmit through the ground. When those forces hit a building, it responds. Since there are all sorts of structural effects that happen (ie, stiffness, damping, mass/inertial moments), the building does not just vibrate with the same frequency of the ground. In essence, the building is a dynamical system of the form [imath]\dot{x}(t)=f(x(t),u(t))[/imath], where [imath]u(t)[/imath] represents the external forcing due to vibration.

There are other effects that introduce some nonlinearities into the system: free-play between stringers and risers in the building, different stiffness properties, etc. And, add to the fact that angular displacement gets magnified by distance.

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