reidential basement floor
reidential basement floor
(OP)
My client who is also the owner-contractor has requested that no reinforcing be specified in the 4” sab in a residential 4-plex we are designing. (a first for me). Any comments about that?






RE: reidential basement floor
We don't design to engineering principles anymore; we design to legal principles.
RE: reidential basement floor
Besides the unsightly cracking and zero resistance to poor base prep there should be no reason it can't work
RE: reidential basement floor
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RE: reidential basement floor
RE: reidential basement floor
Like others have suggested, I think that the key is managing client expectations. I have this conversation with my clients early. Four times out of five they go cheap, and do not call me about subsequent cracks. The fifth time, they go expensive, and nobody harasses me about being a wasteful ninny.
Maybe you should blow your owner-contractor's mind and suggest one of these 3.5" slabs.
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.
RE: reidential basement floor
RE: reidential basement floor
RE: reidential basement floor
A 4" unreinforced slab on grade that is not acting to support structural members above, should work fine if there is a proper compacted granular base, a competent native undisturbed soil with no soft areas, that has been inspected and approved by a geotechnical engineer, no water problem or uplift, not some very unusually heavy concentrated load, and the concrete mix is properly proportioned without too much water.
If the forgoing conditions are not met, then you are kidding yourself if you think rebar will make it ok. Keep in mind that all concrete cracks due to shrinkage, irrespective of whether it is reinforced or not.
A disadvantage of the rebar is that if you ever have to break thru the slab to get at leaking underground drain piping, as I have has to do, it will be more costly to do so because they will have to cut the rebar. I would not put rebar in, not because of the cost, but because it will be of only marginal benefit and will not meet Code for required cover, if the slab is 4".
RE: reidential basement floor
The slab is likely being placed on a vapor barrier on washed stone. As such, it is likely not considered cast against soil
RE: reidential basement floor
In my (limited) experience, the provisions for slabs against soil vs form are due to the roughness of the material. Placing bar 3" away from soil runs under the assumption that the mean distance between the soil and the bar will be 3", and the minimum 1.5". With this in mind unless the washed stone bed is very smooth, I would count it as against soil.
RE: reidential basement floor
RE: reidential basement floor
As ajk1 stated, provide a uniform subgrade and place concrete as dry as practical. The modulus of rupture is about 12-15% of the compressive strength of concrete. The wetter the concrete is placed the weaker the slab will be in flexure. Plus all the other disadvantages to wet concrete, like increased permeability.
RE: reidential basement floor
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.
RE: reidential basement floor
RE: reidential basement floor
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.
RE: reidential basement floor
RE: reidential basement floor
Rittz