Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: mass vs vibration

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Your statement that "mass makes the situation worse, not better" seems
contradictory to the rule of thumb to make the mass of a foundation at
grade several times the mass of vibrating equipment.  Please clarify. 


Bill Sherman
CH2M HILL / DEN 
720-286-2792 

-----Original Message-----
From: Christopher Wright [mailto:chrisw(--nospam--at)skypoint.com] 
Sent: Saturday, July 15, 2006 12:20 PM
To: seaint(--nospam--at)seaint.org
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/


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********