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Concreting stair and walls in one single step

Concreting stair and walls in one single step

Concreting stair and walls in one single step

(OP)
Hi,
Regarding the fact of concreting slabs and vertical elements at the same time, i would never recommend it because of plastic settlement which will occur.
However the contractor is asking to pour concrete a hellicoidal stair and it is landing with the adjacent walls. The walls are 3 m height and the stair isnt that big.
Do u think i will always have a settlememt problem or will it be okay for a small area ?
Thank u

RE: Concreting stair and walls in one single step

I believe that plastic settlement issues are more to do with vertical element behaviour than horizontal element behaviour. As such, I doubt that the small area of the horizontal pour really alleviates the concern. Revibration also probably isn't a remedy as your slabs are likely to thin to vibrate/revibrate.

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: Concreting stair and walls in one single step

(OP)
Thanks kootk. So it is ok to pour all together ?

RE: Concreting stair and walls in one single step

No, I was actually saying the opposite geo321. My argument was that I saw no reason for the small area of the pour to justify that there won't be plastic settlement cracking. That said, I'm not sure if you'll have problems. In retrospect, I've had number of plinths installed as single pours that exhibited no issues. Those would have been little slabs on walls on the order of 15'x15'x5'. We recently also discussed tunnel forming here and the poster indicated that he's done that in the past without issue.

To be honest, I was hoping that hokie66 would show up on this one and render a verdict. Most of what I know about plastic shrinkage settlement came from him an the following documents:

CCAA
NRMCA

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: Concreting stair and walls in one single step

I think in this case the possibility of a gap due to plastic settlement can be avoided easily. The stair and landing will be supported on the formwork, so the only issue would be where the landing bears on the wall. Just make sure that the wall concrete is compacted well, and then revibrate through the landing concrete into the top of the wall.

Where I have seen examples of plastic settlement, they have invariably been in large placements, where the quantity overtook the quality. That need not be the case for your stair.

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