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RE: Dynamic design of machine foundation

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Rich,
In addition to the references previously cited, I have used Foundation Engineering Handbook, by Winterkorn and Fang, reference Chapter 24 Foundation Vibrations by Richart. It quantifies a lot of subjective information and presents it very well.

As was pointed out, acceptance criteria is critical. I have had acceptance criteria submitted in all shades of vague. Acceptance often varies depending on the nature of the forcing function. I have had very brilliant dynamicists not have a clue when it comes to seismic accelerations. When anything goes wrong with a machine, you can be sure that it was the foundation stiffness will be blamed for the problem.

And it should be noted that not all geotechs are equal in providing meaningful information. When response and acceptance criteria are VERY critical ( i.e. 4 micro radians of maximum movement due to proximal equipment and peripheral vehicular traffic), I use a company called Geovision to analyze and characterize the soil. Those guys spoon feed me so that I look like I know what I am doing. They boost me up that Socratic search for smarts. On one huge project they located a fan on an HVAC unit in an adjacent building that was broken in a kind of "oh by the way" manner.

Regards,
Harold Sprague




From: "Rich Lewis" <sea(--nospam--at)lewisengineering.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: Dynamic design of machine foundation
Date: Mon, 13 Dec 2004 14:49:44 -0600

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
rlewis(--nospam--at)lewisengineering.com




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