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RE: Dynamic design of machine foundation

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Richard,

The operating frequency (n) is the first harmonic and
2*n is the second harmonic. The primary and the
secondary forces you have noted correspond to these
two frequencies. The secondary forces come in to play
only in reciprocating compressors.  Vibratory forces
from centrifugal machinery are functions of 'n' only.
If the machine vendor has given you both the primary
and secondary forces, the machinery is, most probably,
 reciprocating. One of the mechanical engineers in the
list may clarify.

Suresh et al's book is a good one. I am glad you
ordered it.

rajendran

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

> 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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