Rigid Foundations for Dynamic Equipment

[JAX91]

My company uses an old design guide to engineer foundations for dynamic equipment. The design guide assumes the foundation is rigid. To make the assumption that the foundation is rigid, the guide recommends providing a foundation thickness greater than or equal to 2’-0” plus the longest mat dimension divided by 30 (2+L/30). This seems a bit excessive, especially when you have a long skinny piece of equipment. I am currently design a foundation for a turbine driven compressor. The skid is roughly 64’-0”x9’-0”. I plan to provide a foundation that is 66’-0”x11’-0” in footprint. In order to meet the recommended rigidity requirements, I would have to make this foundation 4’-3” thick. The dynamic equipment on the skid weighs roughly 86,000 pounds. Using the old rule of thumb to provide a concrete mass equal to 3x the mass of the centrifugal equipment, my thickness would only need to be 2’-4”. According to the guide, however, this would not be rigid. Does anybody have a good reference on how to size a foundation to ensure that it is rigid? Or a good reference for designing dynamic equipment foundations?

 

[smb4050]

Supporting soil properties affect the foundation thickness. ACI 351.3, Foundations for Dynamic Equipment is a good reference, and chapter 4 specifically discusses/lists rules-of-thumb method.

 

[TLHS]

How much of that skid is actually the dynamic equipment? I think a 28" foundation would look incredibly small under a 64' long skid if the equipment is actually a reasonably large part of that length. How tall is it? I'm guessing that your little formulat there is doing some approximation to make sure your foundation will rock as a whole unit. The API guidelines do a similar thing by projecting a triangle out of the centre of gravity of the equipment.

 

[charliealphabravo]

The rigidity of the foundation is relative to the applied loads. If you know the characteristics of the actual dynamic loads then perhaps you can do a rational design rather than a prescriptive design which is often overly conservative. My guess is that your turbine compressor runs very smoothly as compared to some type of reciprocating pump. A compressor of that size should come with pretty detailed dynamic load curves.