Assistance with foundation specifications for industrial machine.

[fastline12]

Machine is approx 60K lbs. Layout drawings are somewhat vague and our PE does not do this work commonly.

Here are the parameters I have for now.

Min soil bearing load 3000lb/sf
Min concrete strength - 3000psi
Min foundation stiffness - 5 x 10^6 lb/in
Mod of elas E = 2 x 10^6


I realize the footprint will play into this. Just need a little guidance and general advice.

 

[JoshPlumSE]

You didn't say what kind of equipment you were dealing with, though industrial machine may suggest that it has a dynamic loading. If so, there is an ACI document (351.3R) on the design of foundations for dynamic equipment. You might want to take a look at that document as it gives a lot of good, generalized advice.

At the very least you need to know the operating frequency of the equipment and the unbalanced forces. My belief is that this will fall outside the "light equipment" range where the foundation design is very easy (maximum of 6 kips or so in weight and 200 hp or so). If so, (and assuming your equipment is truly dynamic in nature), you may want to hire a different PE who specializes in this type of foundation design.

 

[fastline12]

Thank you but due to the nature of this install, this is a perfect opportunity to work with foundations.

The operating frequency is unknown at this time and not quite sure how we would determine that. It is indeed a dynamic load as a machining tool.

I have examined the minimum recommended subgrade specs at only 3000psf/in or 21pci That seems very low IMO.

I am gathering data and not the one who will run the calcs but I want to opportunity to learn from this experience. We might consult a local geotech with our data but would rather run the calcs and see what we determine first.

 

[SlideRuleEra]

fastline12 - Since this is a learning opportunity for you, take a look at the items on this page of my website:

http://www.slideruleera.net/foundations.html

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[John2025]

We have a few CNC machining centers, albeit only about 20,000 lbs. They all came with foundation specs and mounting requirements in the installation section of the maintenance manual including thickness, rebar, etc. I'd start there.

 

[fastline12]

John, we have every detail of paperwork produced and all we got was what was posted above. It is now being assumed that any additional foundation would have to be for damping since machine support seems very easily covered with decent subgrade and 12" of concrete.

I am in contact with the OEM now to determine why there is little detail on this.

 

[John2025]

Huh, that's not much to work with, is it? FWIW, here's a dwg from a 16,000 lb machine.
Good Luck.

 

[dhengr]

Fastline12:
Your interest in learning something new is admirable, but this a significant enough problem, and a rather specialized area of practice, that you might learn best, quickest, and by doing the least damage, if you study the results of someone who really knows what he is doing on this problem. The operation/performance of your expensive equipment, the productivity of your shop and the quality of your finished product have something to do with the foundation under your machine, and it should certainly not be jumping/bouncing/vibrating/flexing around during operation. If your P.E. doesn’t commonly do this kind of work, a nice way of saying he doesn’t want to chance tackling this found. design problem because he doesn’t know how, not a disgraceful admission; you are a brave (maybe foolish) fellow to assume you will do it then. JoshPlum’s advice and admonitions are right on the money, you might do well to heed them.

 

[fastline12]

I don't have time to discuss every detail but basically, this is an old machine and we know as long as things are close, it will work fine.

HOWEVER, I finally got a print of the foundation specs!!! They call for 16" of crete with specific rebar placement and such, all we need! However, they are creating a full isolation pad and we now realize what is happening. They want to create a stiff, isolated pad with enough damping for the machine so that any neighboring machines will not affect it. However, the OEM has to make assumptions in shops and the only way to fully protect it is an isolation pad.

However, this shop does not have anything around that would affect the machine to a large enough degree that we would ever see it! I think we can follow the OEM recommendations on the pad but I am resistance on making it isolated. I would rather bar this with the rest of the floor to add damping.

We are still just discussing it and I am sure few here would even consider doing anything except precisely what the OEM recommends but..... has anyone done machine foundations like this? I know of several of these machines that were literally just installed on 12" floors and run great!

 

[John2025]

We routinely bolt smaller machines to our 5" floor and call it a day. We'll get closer to manufactures specs on bigger or more critical machines. We machine aluminum to pretty wide tolerance and are more concerned with dampening, too. I'd love to isolate and all that, but it's not usually worth the extra cost for our application.

 

[RFreund]

You guys buy these super expensive machines and then are so cheap with the foundation. I never could understand that. I say this light heartedly but I've taken several calls on this before. Every time the shop says nevermind we don't need it engineered, we'll just bolt it to the floor. But you may want to... hello, hello.. and they're gone.

EIT

http://www.HowToEngineer.com

 

[John2025]

I hear you, but what happens in at least our case is that a standard CNC has 30-40 times the accuracy we need for our process so we convince ourselves that we don't need to shell out the money for a massive foundation. One interesting note: when we went to order the hold-down kit for our last machine the manufacturer's dealer didn't even know what we were talking about. They sell very few as most people apparently just set them on the floor and let her rip. Of course it depends on the kind of work you do.

 

[L0k]

use the rule of thumb: your block footing is ranging between 2-5x your machine weight depending on the machine type