Concrete slab thickness vs.footers

[USAFpj]

About to do a 30x40 slab at 4in of thickness; not sure what the PSI rating of that will be. I imagine that when concrete is poured, it is thinner in some areas, and thicker in others. If I eventually want to put a 2 post lift in, the consensus is to go at least 5in in thickness on the slab. However, the company that is building the pole barn says that they just pour a footer in the specific area that you want your lift. So my question is this: should I just do the entire slab in 5in for building integrity, or are the footers enough? I've about maxed my budget with a 30x50x14, so I'm looking to get help where I can.

 

[GPintheMitten]

What are you storing and driving in the barn? How heavy?

If you can identify now where your future lift would be I would go with thicker footings for that at specific area. You also might want to go thicker on the perimeter.

 

[USAFpj]

GP, as of now, I will not be storing anything other than 1/4T jeeps and WWII 1/2T Dodges. I do not plan on having any heavy machinery in the future.

 

[flusher]

Pour 4" thick 4000 psi concrete, #4 rebar grid on 24" centers, 2" dobies to center the rebar vertically.
Use steel plates (24"x24" x 1" thick) under your lift columns to spread the load.

Good luck

 

[Wa11banger]

"(24"x24" x 1" thick)"

Flusher im not the original poster but I have a 4" thick already and was getting ready to do a very expensive retrofit. This will save me a ton of money

 

[GPintheMitten]

Pour 4" thick 4000 psi concrete, #4 rebar grid on 24" centers, 2" dobies to center the rebar vertically.
Use steel plates (24"x24" x 1" thick) under your lift columns to spread the load.

Good luck

That sounds like a good plan.

 

[EddieWalker]

Given that concrete is running about a hundred bucks a yard, it's really cheap to dig a 2x2 foot footing under the place where the lift will be installed. If you have good soil, then a foot deep below the bottom of the pad should be plenty. If you have sand or other poor soils, then you really need to talk to a soils engineer because the variables make impossible for anybody who does not know your soil to be able to give good advice.

 

[/pine]

Agree about what (earth) the concrete is sitting on...
Also, if the steel plate has to be purchased new...it's going to run close to $200 for each plate...hardly cheaper than concrete and rebar...

 

[Wa11banger]

but in my case cutting out a large section, reinforcing it to tie it back in and digging it out is way more expensive than the plate we are discussing.. For the OP it is sound advise.

 

[/pine]

...For the OP it is sound advise...

I disagree...as long as the underlying strata is satisfactory and any disturbed earth is compacted a bell type footing under the support columns is easily the most cost efficient way to go...it is a tried and method that is standard in commercial building applications...