concrete specs for safe

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Old 03-13-12, 07:21 PM
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concrete specs for safe

How much concrete would I need to support a safe that is 72.5" x 42" x 30.5", and weights 1600 lbs?


If you know where I can find a concrete calculator for weight support and requirements (thickness, rebar size, etc.), that would rock.
 
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Old 03-13-12, 08:14 PM
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Where are you going to put this slab? I presume inside so what kind of floor is there now? Is this related to your post: http://www.doityourself.com/forum/br...ete-specs.html?
 
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Old 03-13-12, 08:30 PM
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Yea, it's all kind of inter-related. I have a few things I need to build on different properties. From sheds, cabin, and home. I plan on getting a contractor to do the concrete, and want to make sure we have what it takes to support a large gun safe. Since the weight is not spread out, I'm a tad concerned.
 
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Old 03-14-12, 03:28 AM
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The weight IS spread out over inches. Compressive strength of concrete is measured in square inches. Even very crappy concrete would be at least 2500 psi, meaning it would support 2500 pounds PER SQUARE INCH without becoming pulverized. If you had a 2500 lb. safe supported completely by a 1 inch dowel standing on the floor, the concrete would still support it without becoming crushed.
What you really need to be concerned about is what's supporting the concrete. Is it a slab on the ground, on a wood floor over a crawlspace or basement, or on a second story? You need to make sure your joists or whatever will support the weight of the safe plus the weight of the concrete.
 
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Old 03-14-12, 06:11 AM
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Slab on the ground, we'd never put a safe on the 2nd floor.

In theory, it sounds like 1 inch would work. What thickness would you use?



EDIT: we don't want to put any extra stress, or cause cracking/breakeage, if we put the safe on the corner of the slab.
 
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Old 03-14-12, 08:33 AM
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The PSI measurement refers to surface area, not depth of concrete. Floor concrete should be a minimum of 4 inches thick.
The flexural strength of concrete is lower than the compressive strength, so setting something heavy on the edge of it could cause the concrete to crack as the weight pushes it down. If you're setting the safe in a corner, you should probably use rebar reinforcing under it and extending out into the floor too.
 
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Old 03-14-12, 09:19 AM
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The dimensions and weight you mention are pretty common for a gun safe which are sat on normal concrete floors without any special preparation. Your safe is about 1.25 pounds per square inch ground pressure which is less than a adults foot pressure (about 8 psi).
 
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Old 03-14-12, 10:11 AM
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If you do not have good soil support (well compacted) the concrete strength and thickness can mean little. If you do not load the safe uniformly or store a lot of weight, you can easily throw most of the weight on one or two legs. Also, the weight of the safe does not include the contens and anything on top.

I would make sure have a good soil base and just form and dump in a 4" or 6" slab (3000 to 4000 psi concrete is cheap and easy for such a small area) for the safe and isolate it from any surrounding concrete to avoid cracking any surrounding concrete. The idea of 1" is a joke! Concrete is tested in 6" diameter cylinders that are 12" thick and the thickness make a difference since this definitely not a situation of bearing and you are considering a slab.

Also, put in some reinforcement in the slab under the safe to avoid cracking, especially if you do not have as good soil base as you think.

You never know what will happen with concentrated loads near the edge or corner of a DIY slab.

Dick
 
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Old 03-14-12, 01:53 PM
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Yeah the 1 inch dowel thing was meant as an illustration of what 1 square inch means...not that anyone would actually do it that way!
 
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Old 03-14-12, 06:59 PM
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Too late, I already bought some one inch squares.


I'm not sure what the normal thickness, or size of rebar (3 or 4?) for foundations in the Houston Texas is and how much it differs, depending on the building (tool shed vs 1 story home vs 2 story home, etc.).

From footings (12" for patio cover) to foundations for metal buildings (32" in some outside spots), that I've seen lately, it's all greek to me.
 
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