Would my foundation be okay?

[Cold Fusion]

I have the chance to buy a 12,000 pound 10'x6' bridge mill and I'm worried about the garage foundation. It's a 4" deep slab with steel mesh. I would be setting it up on the left side of the garage, with a minivan sometimes parked on the right side. It would be centered vertically, but not horizontally because the car needs to be able to get in. Is this going to cause a problem with shifting or even cracking? I figured that the load would be spread over 35 square feet with the cast iron base.

[ger21]

I think you really should have an 8" slab under that. Are you sure the load is spread evenly, and not on small leveling pads?

[HuFlungDung]

It could be a bit dicey, but you never know until you park it

The base is likely hollow as Gerry said, and the machine will sit on levelling pads. You could spread the load by placing a 2x10 plank beneath the pads.

[Cold Fusion]

Hmmm, did not think about the pads. It wouldn't be that much trouble though to setup a load spreading system like HU said.

[ger21]

I know we have some machines at work that weigh less than 12000 lbs, and the manufacturers do spec at least 8" slabs. But I don't really know how much a 4" slab can support.

[Cold Fusion]

I have the chance to pick up a $25,000 mill for $4000, and the only limitation is my concrete

[Alan T.]

Check with your local building code to be sure. I'm not sure its relative but I have a 37,000 lb MRI Scanner and the engineer spec'ed an 18in slab. It would also be affected by the soil compression under the slab.

[sol]

Unfortunately the garage slab was not really designed for this kind of load but...
What the concrete slab rests on is important; if properly set on compacted earth there should be little problem because even soft clay is good for 2000 pounds per square foot.; gravel is good for 5000 ppsf. You are putting "only" 350 lbs per square foot on the concrete The reinforced concrete is not going to compress or separate but it may crack if the sub-grade was improperly prepared and the slab is forced to flex. With the machine being close to the wall and I assume a trench footing the load is going to be further spread which will help.
I'd put a mill in my garage and not worry about it; the worst case scenario is a hairline crack in the slab unless the builder was a real sleaze. Further, if a crack developed I'd rent a concrete saw and cut a score around the machine and let it crack all it wants. Of course your folks may not see it this way.

[Cold Fusion]

Yeah, I don't think they would be too thrilled about me cutting into the slab.

What I really need to do is call Onsrud and get the actual weight of the item. The owner was ballparking so who knows if he's close. Here is a picture of it.

[ger21]

Rent a concrete saw from Home Depot, and cut out the slab where the machine will go. Then either pour a new 8" slab, or put a small footing where each of the machines pads will be and repour the 4" slab. Should be able to do it for $500-$1000.

What about the 3 Phase power you'll probably need?

[sol]

You beat me to it Gerry; that is exactly what I was going to say first thing this morning. I came up with the same price questimate; too... okay so my low end was $300 but same high.
A weekend of hard labor and it would be done "right" with no fear of future cracking.

Good luck CF, I hope your parents go for it...

[ger21]

[QUOTE=sol] I came up with the same price questimate; too... okay so my low end was $300 but same high.
QUOTE]

I recently had a small slab and footing poured for a small addition on my house. The concrete company had a minimum charge of something like $400, so even if I only needed $200 worth, it still cost me $400. That's why I came up with the $500. YMMV