vibrating machine foundation design recommendation 1

[cbailey82]

Is the rule of thumb for rotating machine foundations 3 times the weight of the machine mean 3 times the total weight of the machine (moving parts plus stationary parts) or just 3 times the weight of the moving parts of the machine?

 

[WARose]

The general rule I've used over the years is 5-10 times the weight of the moving parts or 3-5 times the weight of the whole machine. A lot depends on the weights involved.

Keep in mind: that's just a starting point. It doesn't guarantee good performance.

 

[JoelTXCive]

We use 5 times the weight for reciprocating machines (piston engines).

We often do generator pads at water treatment facilities and wastewater plants. We are fortunate that they are generally located out in isolated areas. I will use the 'wet weight' of the generator, which is the generator + enclosure + fuel tank in a ready to run condition. It does NOT include the actual fuel though.

There are two design documents that can serve as a guide. I think there are older versions of the documents on the internet for free. Look for:

ACI 351.3R Foundations for Dynamic Equipment (it was just updated in 2018)

API/PIP 686 Recommended Practices for Machine Installation & Design

 

[Tmoose]

A ways back ACI " Foundations for Dynamic Equipment " was a collection of individual papers.
Some pretty much began and ended with the "foundation weight should be X times the equipment weight."
There was only one that emphasized that it was vitally important the "width" of the foundation slab should be something like 2X the height of the shaft CL above the foundation, and sometimes much wider if the soil is poor. And of course the thickness of the foundation must be sufficient for all the imposed forces.

https://gharpedia.com/wp-content/up...Collapse-due-to-the-Foundation-Failures-2.jpg

 

[WARose]

Yes, there are a bunch of rules of thumb with this stuff. Thickness (in part due to localized deformation; which would make the Single Degree of Freedom Model worthless), width (which helps with the rocking motion), etc, etc.

But I've seen these "rules of thumb" get people into a lot of trouble. You have to really be careful with this stuff.

Another one I see people do all the time is: they treat the calculated spring constant like it's 100% accurate. It isn't. The actual value will fall within a range of possible values. (Depending on the geotechnical work done.)

 

[TEDstruc]

The attached reference has a good amount of information as well some design examples.

 

[TEDstruc]

Here's another reference. This is a powerpoint presentation from a seminar I went to. If you read through it, they give some rules of thumb for weight and dimensions.

 

[cbailey82]

Thanks to all that responded. I appreciate it.

 

[ThomasH]

In my experience the manufacturer of the machine often har requirements for the foundation.

Avoid a specified frequency range. That is usually depending on the machines speed.
Limitations in allowable vibration levels.

But it depends on what type of machine. Can the machines vibrations have negative effects on the surroundings?
It can be a long list if you want to include everything.

Thomas

 

[robyengIT]

excel software

https://www.excelcalcs.com/repository/dynamics/machine-foundation-analysis-and-design/

and some literature attached (found all over internet)

https://mega.nz/#!1JlzTLJb!0tCcWFv_YrC-LeTgxrWgnfg2TD6uy4novDABjTIlVb8

 

[mck26]

What is everyone's position on isolating vs tying in a machine foundation to the adjacent slab on grade (with dowels)?
We prefer to isolate and install unisorb pad but machine specifications recommend dowel into adjacent slab.

 

[WARose]

What is everyone's position on isolating vs tying in a machine foundation to the adjacent slab on grade (with dowels)?

Something to be avoided. You can much more efficiently address it by having that mass included in the support block (and control displacements at the source). Something like that would unnecessarily complicate the analysis.

 

[BUGGAR]

When CRSI had their design competitions (in Basic), they published the winners. One was for a vibrating machine foundation. I entered the contest because it got you a free CRSI Manual and copies of all the programs. I still have a copy of Vibe.bas but no Basic to run it on.

 

[human909]

I'm far from an expert here, but.....

Rules of thumb would only be vary vague approximations and could very easily lead you to over-engineer or under-engineer a design. Already in this thread there is mention of a "rotating machine" and then others mentioning reciprocating machines (piston engines) which are a fair bit different.

And then there is frequency... With some machines, weight has very little to do with the design. You need to avoid particular frequency ranges so that might involve making you structure far stiffer than would otherwise be needed.