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RE: seaint Digest for 13 Dec 2004

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For pump installations it is common to provide 2 to 3 times the
equipment weight in foundation and base support to dampen vibration when
the pump runs out of balance.  This may not be directly applicable for a
compressor but I used the Ingersoll Rand installation reference that I
used a few years back for a compressor and believe that it recommended
similar damping mass.  That compressor weighed at most 5K.  With a 130K
piece of equipment that would be about 64 cu-yd of concrete.  With the
30 x 40 foot required area that is only a 9" slab.  A common raft
footing is the way to go, it should minimize differential settlement.

Craig Hawe
Norwest Corporation

-----Original Message-----
From: Rich Lewis [mailto:sea(--nospam--at)]
Sent: Monday, December 13, 2004 12:50 PM
To: seaint(--nospam--at)
Subject: Dynamic design of machine foundation

I am designing a foundation for a 130,000 lb compressor with dynamic
loads.  The foot print of the equipment is over a 30X40 ft. area.  It
will have a separate mat foundation below it.

I have done some research and it appears to me a dynamic load such as
this requires a special analysis to calculate the deflections based on
the dynamics.  I found several references on this, one in particular by
Bowles in the 5th ed., chapter 20.  He has a program to calculate the
vertical, horizontal and rocking deflections due to the machine
dynamics.  Is the method he describes in his book what is commonly used
in practice today?  Is there an easier way to do this?

Bowles method requires the dynamic shear modulus.  Are there some tables
with typical values for clay soil other than what he has in his text?
Bowles uses primarily metric in this chapter and doesn't have an
equation for English dynamic modulus.

I would appreciate any suggestion I can get for foundation design of
dynamic equipment loads.

Richard Lewis
Lewis Engineering

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