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RE: Dynamic design of machine foundation

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Rajendran,

Thanks for the information.  I assume it is a centrifugal.  It has a
spinning drive shaft run by an electric motor.  I assume by
reciprocating is like an eccentric wheel spinning.

I'm not sure what you mean by first and second harmonics.  I have
primary forces and secondary forces.  These are forces and moments.
There is a constant RPM of the machine.

I do have on backorder "DESIGN OF STRUCTURES AND FOUNDATIONS FOR
VIBRATING MACHINES" by Suresh Arya, Michael O'Neill and George Pincus.
It will take several weeks to get it as they have to photocopy it since
it is out of print.

My Geotech is not too helpful.  Apparently this is the first time anyone
has asked them for the dynamic shear modulus.

Rich


-----Original Message-----
From: Padmanabhan Rajendran [mailto:rakamaka(--nospam--at)yahoo.com] 
Sent: Monday, December 13, 2004 3:05 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Dynamic design of machine foundation


Is it a centrifugal compressor or a reciprocating one?
It is important to know which one it is. With a
reciprocating compressor both the first and the second
harmonic needs consideration. The operating frequency
of a modern day recip compressor is fairly high and it
will be a challenge to size a suitable foundation to
assure that the sytem frequencies are well separated
from the operating frequencies.

There must be a geotech report to enable you to design
this foundation. If there isn't one, please request
it.  This foundation is a critical component of the
machine foundation system and an improperly deisgned
foundation will create problems with the machine
performance.

The geotech company should be able to give you a range
of presumptive values for the dynamic shear modulus,
based on the soil log data. It is a key parameter in
the dynamic analysis and has a significant bearing on
system frequencies.

By the way, you need more literature than just the
book by Bowles.

Rajendran


--- Rich Lewis <sea(--nospam--at)lewisengineering.com> wrote:

> 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 l

oad 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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