Foundation for Machinery

[maneesha0702]

There is an empirical rule that the weight(mass) of the foundation needs to be 3 times the machinery (API). How should the weight be calculated? Is it below grade only? If so is there any clarification any write up or commentary any where.

 

[oldestguy]

Usually the dynamics of the machine control. If it has much imbalance, a massive foundation may be needed. If none, maybe just the floor slab. Weight controls then.

 

[MJCronin]

It is my understanding that the following references the book that best covers machinery foundation design.

http://www.amazon.com/Design-Struct...4&sr=1-4&keywords=machinery+foundation+design

Also, it should be remembered that the machinery vendor clearly bears some responsibility in the foundation design details.

Competent and first class pump vendors, such as Goulds and Flowsereve provide detailed requirements in their O&M manuals.

Whereas in the third world, there exists an active market in used equipment, there will always be a problem because all documentation has been usually thrown away by the previous machinery owner. This, of course, makes things extra difficult for the hapless newly graduated engineer who is assigned the foundation design for the used equipment.

The distinction must be understood between "reciprocating" equipment (which generates high and harmonic vibration) and smooth running "centrifugal" types of equipment

MJCronin
Sr. Process Engineer

 

[KootK]

ACI 351 might be useful to you. Logically, I can't think of any reason why effective mass should be limited to mass below grade. The mass will effect the K/m ratio whether it's above grade or below.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Denial]

Mass embedded in the ground is no different from mass above ground as far as sqrt(K/M) effects go.[ ] Its particular benefit comes from the additional damping it usually offers, by engaging "radiation damping" in the soil.[ ] This can be useful if you are getting a bit close to resonance.

 

[Denial]

When composing my post above I forgot to add a strong endorsement of the reference book MJCronin is suggesting ("Design of Structures and Foundations for Vibrating Machines" by S.Arya, M.O'Neill & G.Pincus).[ ] You won't find better.

For vibrating machines on a rigid concrete pad footing, the book's Table 6.2 contains a step-by-step method of analysis.[ ] I have written a spreadsheet implementing this method, downloadable from my website (rmniall.com).

 

[Angre]

The response of the structure to dynamic loads depends mass and stiffness of the structural system.
Ideally since the soil is also a part of system, it's mass would also play a part, but it is convenient to ignore it due to it's minor stiffness.

coming back to your question, the mass of the footing both above and below the grade should be considered.

 

[JoshPlumSE]

I would point you towards ACI 351 as the most practical reference. Really probably the best place to begin. It focuses mostly on exactly what is done in engineering practice. Then it points back towards other sources for references for the theory behind the methods presented.

I've got nothing against the S.Arya, M.O'Neill & G.Pincus book. It is a fine reference as well. And, anyone who wants to become an expert on this subject will want this as a part of their library. But, it's more theoretical than practical. As such, it may be a bit intimidating to someone who isn't already well versed in the subject.