Engine generator foundation rules of thumb - does vibration isolation change the situation?

[Dennis59]

For decades, the standard rule of thumb on a concrete block foundation has been 3 to 5 times the weight of the machine.
I have never really seen it clearly stated as an assumption, but I have always assumed that the underlying assumption is that this is valid when the equipment is solidly anchor-bolted down to the foundation.

I have personally seen installations of CAT 1600 KW landfill gas engine generator skids (Engine 3520) sitting on top of a series of amazing vibration isolation pads with the skids themselves not bolted down to the foundation at all. And the foundation was more on the order of 1 times the weight of the genset. Vibration on the steel skid was perceptible with my foot but vibration on the concrete pad next to the vibration isolator was absolutely imperceptible.

I have been unable to find reference material that will let me quantitatively design a genset foundation block with the explicit condition that the genset will be sitting on vibration isolation pads.
Does anyone know of such a reference?

Thank you in advance.
Dennis, structural engineer, nearly retired...

 

[oengineer]

This thread contains some information about pump foundation design:

https://www.eng-tips.com/viewthread.cfm?qid=467238

( thread507-467238)

It references ACI & PIP.

 

[r13]

I think the isolation pad is designed to absorb the vibration and resolve the dynamic forces down to static loads, so the lateral load is small compared to the engine weight, thus make it more stable, and the demand of support fixity is minimized. The 3-5 times machine weight rule was intended to avoid resonance between machine operation frequency and foundation period, a rule of thumb by past experiences.

Even with the reduced difficulty, you need vendor furnished reactions, load case, and load combinations to properly select a support system, and design the foundation.