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  1. #1
    Elite Member RonMar's Avatar
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    Default Concrete slab load limits.

    Does anyone have a link to any load limit reference material for concrete slab on grade floors? I have been looking around a bit, but have not had any real luck finding what I am looking for. What I am looking for is typical slab thickness load limits in pounds per square foot. IE: How much of a per SQ/FT load will a 4" garage slab withstand? Or a 6" slab?

    thanks
    Last edited by RonMar; 03-14-2009 at 07:49 PM.
    Ron

  2. #2
    Veteran Member Treemonkey1000's Avatar
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  3. #3
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    Default Re: Concrete slab load limits.

    Compressive strength of concrete for footings to floors should be 2500 -3000 psi or more at 30 days when poured & cured properly. The limiting factor that you need to consider is the strength and compaction of what's under the concrete. On good compaction with non-expansive soil a 6" slab will hold the heaviest equipment , dozers, excavators, etc. If you have bad soil you need a reinforced slab, like a bridge deck on the ground. If you leave marks on the ground before you pour or the ground raises or expands when wet then you'll not be happy with the floors performance later. "Architectual Graffic Standards" is a good reference book for reinforced slabs. MikeD74T

  4. #4
    Elite Member RonMar's Avatar
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    Default Re: Concrete slab load limits.

    Thanks. That is an interesting site, and I added it to my bookmarks, unfortunatly in about 90 minutes looking thru it, I didn't find what I was looking for.

    Perhaps if I lay out the details of the project I am contemplating. I want to add a large super insulated hot water storage tank to an upcomming home build. When I say large, I am talking 750 gallons. That is a tank approximatly 70" in diameter by 45" tall. A tank this size will have a bottom surface area of around 26.73 SQ/FT and the bottom insulated pad will have a surface area of approx 36.67 SQ/FT. At around 6400# all up tank weight when full, that is a load of 174-239 LB per SQ/FT, depending on how much the lower insulation distributes the load over the floor. I am estimating that the The ground floor/basement level will be a 4" re-enforced slab with footings over 2-4" of insulation, with ICF walls. With the potential load and footprint from the tank described above, does anyone think the area this tank will occupy will require any additional floor thickness? Is there a "rule of thumb" that says in general, do not exceed XXX# per SQ/FT on a 4" slab.

    Thanks
    Ron

  5. #5
    Elite Member RonMar's Avatar
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    Default Re: Concrete slab load limits.

    Quote Originally Posted by MikeD74T View Post
    Compressive strength of concrete for footings to floors should be 2500 -3000 psi or more at 30 days when poured & cured properly. The limiting factor that you need to consider is the strength and compaction of what's under the concrete. On good compaction with non-expansive soil a 6" slab will hold the heaviest equipment , dozers, excavators, etc. If you have bad soil you need a reinforced slab, like a bridge deck on the ground. If you leave marks on the ground before you pour or the ground raises or expands when wet then you'll not be happy with the floors performance later. "Architectual Graffic Standards" is a good reference book for reinforced slabs. MikeD74T

    Thanks Mike
    I am obviously well within the compressive strength of the concrete itself, but there are indeed a lot of variables, which is probably why I don't ever recall seeing a rule of thumb My future build site is mostly sand and round rock, but I am not sure how that will effect load bearing ability beneath the slab. I am just trying to get my brain around some of the details I am planning for this new home, and wether I need to make special considerations or perhaps make different plans for certain features. A large thermal storage tank has been a dream of mine for quite a while though, as it adds some real versatility to the available forms of energy I can use to efficiently heat in the winter time.
    Ron

  6. #6
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    Default Re: Concrete slab load limits.

    Not sure this helps, but way back when I was renting warehouse space there was a building code or something that said not to exceed ( I think) 100# per sq ft.
    Now this proly has more to do with ocupency code than actual concrete load.

  7. #7
    Elite Member CurlyDave's Avatar
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    Default Re: Concrete slab load limits.

    Ron:

    Proper design will allow you to spread the load out where your tank will be, but the first thing I would do is get an opinion from a soils engineer.

    In my fairly limited experience, I have seen soils that have 2000#/sq ft to 8000#/sq ft load bearing capacity. Anything above 2000#/sq ft is well above what you need for your tank.

    I am sure soils exist that are below 2000#/sq ft, but I just haven't seen them yet.
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  8. #8
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    Default Re: Concrete slab load limits.

    You could do a google search on PCA - Portland Cement Association. They have lots of good slab on grade information.

    You could also do a google search on ACI - American Concrete Institute.

    Joints, temperature & shrinkage reinforcement, subgrade, prep, loading should all be considered.

    I have had several garage slabs installed. For smaller to medium equipment - cars, smaller trucks, nominal rack loading, I used a 5" slab with 4000 psi concrete, fiber reinforcement, and air entrainment.

    Still a few smaller cracks under some heavy loading areas, but overall, very good results.

    Good Luck,

    Yooper Dave

  9. #9
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    Default Re: Concrete slab load limits.

    Hey Curly Dave:

    I engineered a large house that looked like a river paddleboat way down south many moons ago.

    The geotechnical engineer stated that the soil bearing capacity was only 800 psf. Most building codes do not allow you to build on soil with less than 2000 psf bearing capacity. However, way down south the code was not so strict. The footings got real large and expensive.

    Also built several buildings over peat moss - not recommended. The soil bearing capacity was nil, so we had caissons, grade beams, and structural slabs. When location is everything, it only takes lots of money to make the dream happen if the underlying soils are bad.

    Regards,

    Yooper Dave

  10. #10
    Veteran Member foggy1111's Avatar
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    Default Re: Concrete slab load limits.

    I'm not sure of the loading of vaious concrete thickeness....but.....I remember waaay back when I was in my 20's and working with similar inexperienced lads....when we received one million lbs + of coiled steel, and stacked those coils in a pryamid at one side of the building. The soil was all good gravel and the concrete was 6" reinforced. We stacked the steel durning the week....and on Monday, the floor was sunk over a foot. We quickly learned to distribute the load....and the floor "recovered" about 1/2 the settleing.....after removing the load.
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