Reciprocating Compressor Foundation 2

[EngrSTR]

Hello Everyone,

I'm involved in FEED phase of designing foundations for a Recip compressor.
Compressor Data:
Shipping Weight = 150,000 lbs
Operating Weight = 300,000 lbs
Dimensions = 44' x 16'

For preliminary foundation design, per API 618, Recip compressor foundation to have a mass ratio of 5 times. Based on this criteria, the foundation will be around 14 feet deep. This seems like never heard/ used of foundation depths for a recip compressor.

can i ignore skid, bottle weights

Seeking expert guidance and opinions,

P.S: Also referring book by Design of Machine Foundations by Suresh Arya, seems to consider operating weight.

 

[WARose]

You can use the 5 times rule.....but if you are getting a excessive foundation size, you can (as a alternative) use 10 times the rotating parts as a starting point for your foundation weight. Unless other rules (like minimum width/length, frost depth, etc) force you to have a bigger one.

The book you mentioned (by Arya) has good rules of thumb......but a detailed analysis (starting with a detailed geotechnical investigation) will give you the final word if the foundation will be ok.

 

[EngrSTR]

Thank you, Will do a detailed analysis per Arya.

i have looked at a few go-by's for similar sized compressors and they only have 4 to 5 feet deep foundations. Could not find any calc's on them, doubt if there are any.

Wondering what is the industry standard, FEA analysis ? Spreadsheet design of detailed analysis per Arya's method ?

 

[WARose]

Wondering what is the industry standard, FEA analysis ? Spreadsheet design of detailed analysis per Arya's method ?

I've seen/done both. The spreadsheet method is pretty good if the foundation can realistically be reduced to a Single Degree Of Freedom [SDOF] system. And that is always a judgement call. The thickness plays an important role there: if localized deformation is possible.....the SDOF assumption isn't valid. (Then you go with a FEA approach.) Arya has various rules of thickness.

 

[SlideRuleEra]

What is added to make the operating weight (300 kips) double the shipping weight (150 kips)?
Doubling the weight seems out of line.

http://www.SlideRuleEra.net

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[JoshPlumSE]

See ACI report 351.3R on foundations for dynamic equipment. Use this to determine soil springs for a Time History Analysis of your foundation.

 

[Klitor]

Is a good part of 'operating weight' concrete needed to fill in the skid?

 

[bones206]

For the first trial sizing, I would start with a shallow mat foundation 4 to 5 ft thick, with plan dimensions that result in a static bearing pressure that is ~50% of the allowable. Mat width at least 1.5 times the height to the compressor CG.

 

[EngrSTR]

yes good part of operating weight is concrete in the skid, oils, panels, etc

 

[Klitor]

Well there you go, the concrete is not famous for being dynamic machine load

 

[EngrSTR]

hahaa...thing is they are estimating it to be around 20-30% at this time. Have not received a breakdown of loads for the rest (doubt if we receive it at this stage).

How much of other operating loads to consider ? or should shipping weight minus skid weight be used for mass ratio ?

 

[SlideRuleEra]

...per API 618, recip compressor foundation to have a mass ratio of 5 times.
Shipping Weight = 150,000 lbs
Dimensions = 44' x 16'
Have not received a breakdown of loads for the rest (doubt if we receive it at this stage).

There is an easy way, size the inertia block using generally accepted proportions:

1. The inertia block perimeter should be at least 1' outside the machine's footprint.
∴ Minimum horizontal dimensions = 46' x 18'.

2. Minimum thickness = 0.10 x length or 0.20 x width, whichever is greater.
∴ Minimum thickness = 4.60'

3. Weight = 46' x 18' x 4.60' x 150 PCF = 571 kips.
Mass ratio (using shipping weight) = 3.81
Need to increase inertia block mass. Use engineering judgement to increase the most important dimensions.

4. Thickness is most important, for rigidity. Say, thickness = 5.00'

5. Width is more important than length, to increase damping to rocking motion.
Hold length = 46'
Increase width from 18' to, say 22'
Weight = 46' x 22' x 5.00' x 150 PCF = 759 kips.
Mass ratio (using shipping weight) = 5.06

This assumes the center of mass of the compressor is located at the center of inertia block.
Check soil bearing pressure.
There is the initial inertia block size... tweak dimension as (if) more information becomes available.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[EngrSTR]

Thank you SlideRuleEra!

P.S: will try to get more info on the difference b/w shipping and operating weight.

 

[Leftwow]

That stipulation is only the weight of the rotating parts. But it looks like you will have to do a dynamic analysis for crack prevention and soils. That is a huge compressor.