Piers sitting in the existing concrete slab on ground 1

[tngv752]

An owner want to build a one storey house above the existing swimming pool.
Small part on the top of swimming pool will be demolished. The owner want to keep the swimming pool base slab (150mm-200mm thick).
New ground floor of reinforced concrete (RC) suspended slab will be supported by the RC beam and piers. I wonder if these RC piers can sitting on the existing base slab of the swimming pool (there will be some anchor bars between the pier and base slab) ? The swimming pool base slab and wall can be drilled with many holes in order to allow the water to escape in case there may some ground or stormwater under. Is it practical ?
Thanks.

 

[MotorCity]

"The swimming pool base slab and wall can be drilled with many holes in order to allow the water to escape"......huh?

Maybe I'm not understanding the arrangement, but drilling holes in the base and walls of a swimming pool so water can escape sounds like a bad idea......just sayin'

 

[EireChch]

Upload a sketch

 

[Harste]

Hello,

I had a very similar job a few years ago - identical situation.

If you want to found your piers on the swimming pool base slab, you'll need to check punching shear, any transferred bending moments (does the base slab have enough moment capacity?) and the bearing capacity of the underlying soils.

If you don't know the reinforcement arrangement of the existing swimming pool, I would steer clear of using it as structural support. It's much better if you core through the base slab and found your new piers directly into the underlying soils, as an independent structure.


MotorCity - coring holes in the base slab is purely for drainage. These wouldn't need to be very large at all, so structural integrity will be fine. Since the OP will be covering the existing swimming pool with a concrete slab, they can't rely on evaporation to dissipate any pooling water. One thing to be careful of is the current location of the water table. A geotechnical investigation will most likely be required.

 

[oldestguy]

I'd place a footing on that slab for each column and be done with it.

Edit: What size for the footing? If one knows the approximate load from the column, one also needs the "bearing capacity" of the slab. Well we know it once had water to "compact" ground some. The slab under the footing will spread out the load some also. I'd have no qualms then about using a bearing pressure on the slab at 2,000 PSF which even works on petty bad soil. A little more scoop and 4,000 psf may work.

 

[PEinc]

I agree with oldestguy about adding column footings. You can also break out some pool slab concrete to get an idea of what reinforcing steel may be present. It might be better to do more than just drill drain holes in the slab. Why not break up the slab, at least in its deepest area? Or, don't break up the slab but use the pool as a crawl space beneath the suspended slab and maybe install a sump pump?

http://www.PeirceEngineering.com

 

[tngv752]

I agree with Oldestguy to provide a footing above the slab for each column. Of course , I provide some bars drilled and epoxy into the slab to hold the footing and slab. By this way, the load can be spread out under the slab and give lower pressure on the soil.

The pier will be 400mm diameter. Max. working load on each pier = 90KN (compression only)
Pad Footing under the pier is 800mm x 800mm x 300mm thick.
The slab is assumed to be 150mm thick with S12-200 central both ways.
Soil bearing capacity under the slab is 100KPa.
Loading area on soil is 1100mm x 1100mm = 1.21 sqm or 121KN loading capacity.