Foundation Natural Frequency
Foundation Natural Frequency
(OP)
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?






RE: Foundation Natural Frequency
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 Machinesby Arya, Oneil and Pincus.
RE: Foundation Natural Frequency
RE: Foundation Natural Frequency
RE: Foundation Natural Frequency
RE: Foundation Natural Frequency
RE: Foundation Natural Frequency
It occurs to me that you might have a reasonable estimate of the spring constant of the foundation, but finding the effective mass (concrete plus effective weight of soil that moves with it) would be the problem. If you neglect the soil weight and figure the natural frequency without it, that should overestimate the natural frequency. If reducing it would move it farther away from the frequency of your motor, that's all you really need to know. Or, if it is a lot different, that's probably close enough. But if the frequencies are in the same ballpark, or adding additional mass would move them closer together, then it would need closer analysis.
It also occurs to me that you could have natural frequencies vertically (which I assume is the main issue), laterally, and rotationally in three directions. There, the book would be useful to see what modes ought to be checked.
RE: Foundation Natural Frequency
"Don't Gamble on Machinery Foundations"
"Principles of Foundation Design for Engines & Compressors"
"Basic Vibration & Vibration Isolation Theory"
on this page of my website:
http://www.slideruleera.net/foundations.html
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Foundation Natural Frequency
fluor has a good design guide for pump foundation. the formula for natural frequency for pump foundation is
Fn = 60/2phi * sqrt (k/m)
RE: Foundation Natural Frequency