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Re: big dig structural failure - epoxy anchors overhead supporting gravity

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Chris,
 
This is not how I understand it. With bridges, for example, there are two criteria to limit vibrations - one based on rigidity (natural frequency) and the other one based on the mass of the structure.  
 
Steve Gordin SE
Irvine CA
 
----- Original Message -----
Sent: Saturday, July 15, 2006 11:20 AM
Subject: Re: big dig structural failure - epoxy anchors overhead supporting gravity


>> (it was written somewhere that the ceiling was that heavy to prevent
>> vibrations)
Whoever wrote that may have been looking for an excuse. Additional mass
does not prevent vibrations. Vibration occurs when you have a mass
supported elastically. More mass reduces the system frequency, but
tends to make the amplitude higher for a given excitation and increases
the dynamic loading. Additional mass makes the situation worse, not
better.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania
1864)
http://www.skypoint.com/~chrisw/


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