Foundation Natural Frequency

I’m designing a pump foundation and need to see to it that the pump’s operating speed is 33% removed from the foundation’s natural frequency. The preliminary design of the foundation is a simple block of concrete, about 10.3’ x 4.3’ x 5’ deep. How to determine the natural frequency? Are soil properties involved?


Depends on how sensitive the piece of equipment is, really. Typically for a typical industrial motor/pump application, I will design the foundation 3x the weight of the motor.

Alternatively, if you are designing a foundation for a generator (high $$ equipment) you may want to consider the soil properties as well. A good reference book would be Design of Structures and Foundations for Vibrating Machines by Arya, O’neil and Pincus.

Above is a snippet.

Another source of info can be found here:

I have had a discussion recently where a 16 MW synchronous motor sits on a 7 or 8 ft high “foundation”. Everything starts shaking so you can see the amplitude from the fuzziness. Luckily, the main breaker tripped after some minute before everything came apart.

OK, you say. Motor not bolted? Severe imbalance? No, but the “foundation” was made from U beams and no damping whatsoever provided.

The guys now think that the motor is at fault, badly built or whatever. They obviously didn’t think about resonances at all and applied a 6x or so “safety factor”, like a bridge has. They were so convinced that everything was OK - except “that motor” that was so inferior. I need to say that the motor manufacturer has built motors for more than 100 years and has a very good reputation. One of the top ten (five, perhaps) in the world.

I didn’t get any decent pictures - “What do you need pictures for?” So you have to trust me. Never seen such an incompetent bunch before. Never.

I really hope that I will not be involved with those guys again. At least not before they learn their trade and get some experience.

“Concrete? Why? Steel is stronger” When you hear such things, you know that there’s no help for them. Maybe they are all MBA:s?

It’s not the MBA ‘s. They just need to go to Mass more often…

Took some time to get the hidden message.

Yes, absolutely. They need to add lots of Mass. Or use concrete. What they have now looks like a small gantry crane. With wheels welded to the rails and motor/compressor on top of it.