What is rule of thumb - Weight of concrete base for fans

Randall's Reliability Driven Pump Handbook page 117 states:
quote:
Some conservative rules of good foundation design include:
1. The mass of the concrete foundation should be 5-10 times the mass of the supported equipment.
2. Imaginary lines extended downward 30 degrees to either side of a vertical line through the machinery shaft should pass through the bottom of the foundation and not the sides.
3. The foundation should be 3" wider than the baseplate, all the way around a pump up to about 500 hp, and 6" wider for larger pumps.
API 686-1996 ("Recommended Practices for Machinery Installation and Installation Design") States:
quote:
2.4.2 A machinery block foundation supported on soil should have a minimum mass ratio of three times the mass of the machinery for centrifugal machines and five times the mass for reciprocating machines, unless analysis demonstrates that a lesser value will perform adequately. A block foundation subject to vibrations may require a dynamic analysis to ensure that the provisions of 2.2.11 are met.
Note: The minimum mass ratios 3:1 and 5:1 are traditional empirical values for foundation mass to equipment mass that should be used unless a lesser amount can be demonstrated to perform adequately. Although the 3- to-5 mass ratio has been a good rule of thumb, in certain installations a dynamic analysis of the rectangular concrete foundation may be necessary to adequately predict its behavior.
Stan,

I have a customer that laid (4) 2 X 10's out on the ground and poured them full of concrete. Didn't even level it off or screed it. then installed a fan (probably 1500 - 2000#) on top of it, put some 1/2" Hilti anchors in it, and called it good Eeker

It is not.

Dave
Stan,

Yes, the 2 X 10's are still on Big Grin
The Hilti's were the first thing to go, I think they are on the third try with anchors (they not only pulled out, but broke the pad where a couple go in). The legs had broken welds.
THis fan is in resonance. When I balanced it (1725 rpm, MOTOR AT 1789), I was bringing it down .2 mils at a time with a grinder just hitting the blades and the weights that were on there. It's sensitive Razzer

Dave
I was called to "balance" a wood hog. This was a laminated disc-type rotor and they had replaced the knives and disassembled the laminations without marking, then reassembled.

Amazingly enough, it was out of balance. It was anchored with 3/8" "thunderstuds" to the 4-6" thick concrete floor. Edited to substitute "had been" for "was" in the previous sentence. Wink

I don't know what became of it. I gave him an estimate of what it would take to fix it and he never got past just the cost of balancing, much less digging a hole and putting some concrete under the thing.

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