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#7286 06/18/06 11:37 AM
Joined: May 2006
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rajbeer Offline OP
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My question is that going by the definition of time period that is,
"the time required to complete one oscillation".

Now, if I say the best option for an engineer should be that , the building should not oscillate , am I right?

That could happen if the time period of a system is very large, right?
Because, if the time period is LESS, the frequency is MORE, hence the system would suffer more oscillations , right?So to make the building suffer no oscillations/ less oscillations the time period should be LARGE.

SO AM I RIGHT IF I SAY LESS STIFFNESS AND MORE MASS WOULD BE THE IDEAL CONFIGURATION?


Raj
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#7287 06/19/06 04:57 AM
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Mostly no.......
More mass and less stiffness ultimately leads to collapse.
Unless you can find the (unobtainable) building material of infinite stiffness, any structure will have an intrinsic period of oscillation.
The trick is to make that period so different from likely inputs that feedback cannot develope..
Check out the CitiBank Tower in N.Y.C.
They had to install a damper to make that one work.

#7288 06/19/06 06:00 AM
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Megastar
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all building that are exposed to the wind have to handle the changing presure in one form or another. in towers as they are made today, they have to dampen out those presure changes internally. i believe one day they will make building interconnected so that the pressure will be transmitted into the ground.


the more man learns, the more he realises, he really does not know anything.
#7289 06/19/06 04:02 PM
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The engineering solution to objectionable resonance is passive and active damping. Your car keeps its wheels on the tarmac and affords a nice ride in part because dashpots and springs (e.g., MacPherson struts) critically damp oscillations from impulse loadings. Skyscrapers can have active damping systems on their roofs.

You don't compromise a whole structure to address one discrete problem. You build a proper building as an overall solution and address its ancillary problems separately.


Uncle Al
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http://www.mazepath.com/uncleal/qz3.pdf

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