Thin Concrete Slab with Edge Compression Loads

[MrEngineerUS]

I have a rectangular concrete slab on grade that will need to take a uniform edge compression load. The load is about 1k/ft and the slab dimensions are about 10'x35'. The slab's sole purpose is to take this compression load and act as a surface to cast a structural slab against. It is desired that the slab be 4" thick but could get away with a 6" slab, if necessary.

My gut tells me the 4" slab with minimum reinforcing will be fine to take this load. But, I can't seem to find a good way to put some numbers on this. I thought about designing it as a wall with the self-weight being supported by the underlying soil.

Any guidance on how'd you attack this? Thanks!

 

[KootK]

I think that you'll be fine with 4" too. I'd treat the SOG as a series of un-reinforced columns pin connected at assumed crack locations. The trick to maximizing capacity will be accounting for the fact that the slab can only buckle upwards, in a direction opposed by the weight of the slab on grade itself.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[manstrom]

If it's picking up loads, it should be a footing and extend to frost depth. There *should* be some kind of break between the footing and slab.

Under 400sf doesn't require frost footings in some jurisdictions, but if you don't do it, it won't be level next spring.

Sounds like this is a shed type structure. If you / they want to skimp on concrete, maybe do a 12" turndown at the edge and thin it out to 4" in the middle.

Manage expectations: this is cheap and easy, but it may crack. Is that ok?



When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[KootK]

Also:

1) What the heck is this?

2) Is there a compression reaction at the other end of the slab or is it a distributed friction on the bottom of the slab?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MrEngineerUS]

Yeah, this is kind of a crazy project. The 4" slab will essentially replace the bottom row of temporary walers in a cofferdam-like system or braced excavation. So, the reaction load from the sheet pile wall is acting as a uniform compression load that runs the full perimeter of the slab. The slab can crack, eventually. It is essentially serving as a form for the concrete slab and walls that will be cast on top of it but once those are in place this slab won't matter anymore.

I looked at a wall design per ACI318, Ch. 14, and with a 4" slab (K=1.0) I can get a 6k/ft design axial strength using Eqn. (14-1). Definitely not an ideal analysis but it does put some numbers on it at least.