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Warehouse floor slab thickness 1

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CardsFan1

Structural
Mar 6, 2018
49
What thickness of warehouse slabs are you engineers out there using? I am just looking for a gut check, not an in depth discussion on the "art" of industrial floor slab design. :)

I am designing a floor slab to support a 20 kip axle load. I have used the the tired and true PCA alignment charts method and determined a slab thickness of 7". I ran the same analysis in RISA Foundation and found that I can use a 5" thick slab.
It is a large slab, so the thickness has a large impact on quantity.
 
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My gut: I wouldn't think of using a 5" slab with a 20 kip axle load.

Your 7" sounds about right - or at least much better.

 
For warehouse, or general purpose industry buildings, I like 8"-12" SOG thickness for anticipating changes, and double layer reinforcement, if warrant.
 
I like seeing 8" (min) because that also gives you a good amount of embedment if you need to have racking or any other installs.
 
Thank you all for your input. I should say that we are using #4 on 16" EW at the center of the slab. So using the design parameters for unreinforced slabs is conservative.

 
Sawcutting is the #1 item... spacing and time...


Dik
 
Yes...you're 7 inches is about what I would expect. It is a pavement first, a static slab second. If you design it for forklift traffic and relatively high wheel loads, the racking (punching shear) will likely be moot.

as dik noted, make sure the saw cutting is done properly and timely. This will give you better load transfer across the joints and cut down on unsightly "random" cracking. Further, make sure the tolerance on subgrade surface preparation is compatible with the slab tolerance range (-1/4", +3/8" is typical) and that no sharp transitions of thickness changes occur (wheel ruts, shelves, etc.). My specification for slabs on grade has a 5/8" in 10 feet flatness tolerance for the subgrade.

Pay attention to the concrete mix design they plan to use. Use the largest coarse aggregate practicable for the placement. Pea rock, #89 stone, etc. are too small for such an application. #57 stone would be the smallest aggregate specification I would use for the coarse aggregate....use larger if you can get it and get by with it for placement purposes.


 
For thinner slab, pay attention to potential problems suggested by skeletron above.
 
Thanks for all of the input.
I said "warehouse" to see what people are doing "in general" . The actual application of this slab is a seasonal, exterior, event space that the owner wants to drive a telehandler on to aid in erection.

Does that change any of your thoughts?
 
So it will be used as temporary driveway? Just check the maximum wheel load with proper impact factor then. Watch out for beam shear, guess it will govern the design for thin, narrow concrete panels.
 
For light duty use... maybe look into a 6" slab... should work...


Dik
 
If 2 layers of reinfocement was used and at least minimum shirkage reinforcemnt was provided, is it still required to have saw cut?
 
Say slab thickness was 10" or more was used and top and bottom reinforcement
 
In practice we still provide the saw cut joints to minimize stress due to initial shrinkage, as concrete has not stiff enough to pass load to the reinforcement. After this stage, the steel will gradually pick up the task.
 

I'm not sure that's the real mechanism...

Dik
 
Me too. But that's our practice, and so far so good.
 
If you don't want sawcuts for some reason, it becomes much more complex. Minimum shrinkage reinforcement won't help. You would need 3 or 4 times that amount for satisfactory crack width control, along with good concreting practices. Another option is a post-tensioned slab on ground, with about 2 MPa effective compression and a subgrade as frictionless as possible.
 
As a side question - is PT suitable for warehouse/industrial flooring, consider the frequent needs for post installed anchorages?
 
Warehouse flooring, particularly for toxic and hazardous chemicals, is one of the primary uses of PT slabs on ground. As to post installed anchors, the tendons are precisely located, so that should not be a problem. Holes drilled might be, when chemical leakage is of concern. These floors are typically bonded PT, not the unbonded variety used in housing in the US.
 
Hookie, if this slab on grade is supported with drilled piers, will is still require saw cut? I thought if something is considered structural slab and has enough reinforcement, it does not need saw cut/contraction joint.

Do you recommend saw cut joints on slab on grade supporting metal building, regardless if it's waffle slab, supported with drilled pier and has top and bottom rebars?
 
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