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Re: Foundation Vibration Design

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Ted,

The dynamic response of a foundation to vibrating loads is really a 
function of the frequency of the foundation soil system (rather than 
simply the weight of the foundation).  The NAVFAC Design Manual DM7 
has a nice (practical) discussion of the important parameters as well 
as recommendations for frequency separation, etc.

You can change the frequency by altering the mass and stiffness of 
the foundation soil system.  Increasing the foundation weight 
decreases the natural frequency.  Increasing the foundation contact 
area (or improving the soil by grouting) increases the natural 
frequency.  NAVFAC DM7 recommends that the "natural frequency of the 
foundation block soil system should be less than one-half or greater 
than two times the equipment operating frequency."  In most cases 
this is possible.  However, I have seen some cases where the 
practical range of foundation parameters do not quite allow this 
magnitude of frequency separation.

"Foundation Vibration Analysis Using Simple Physical Models" by John 
Wolf (PTR Prentice Hall) provides some guidance for a potentially 
more involved approach.

-Mike Valley

> I think I remember seeing on this list a long time ago some discussion of
> isolated slabs used for equipment support. ...
> ...on the order of four times the equipmtent weight.
> 
> Is a rule of thumb applicable for such equipment support? I have struck out
> in my own library. 

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Michael Valley                                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201