Free standing concrete pool wall thickness

[Buleeek]

Hello everyone,

I am currently designing a free standing concrete pool (water pressure is the only "outside" load). According to my calculations, an 8" thick wall with one (1) row of #4 @ 6" o.c. rebars will withstand the water pressure. For other reasons the owner and contractor wants to do a 10" thick wall. Do you think I should design a second row of rebars (close to the outside face of pool)? I am worried about temperature load affecting unreinforced part of the concrete. Or maybe I shouldn't? Where can I get more practical information about recommendations for installing reinforcement in compression zone of the wall?

Thank you in advance for your input.

 

[dold]

CIP walls 10" or thicker requires 2 mats of steel. ACI 318-11 14.3.4. Not sure if a pool would qualify as a basement wall?

 

[Celt83]

check out ACI371-R16 think it may be more applicable, [URL unfurl="true"]https://www.concrete.org/Portals/0/Files/PDF/Previews/371R-16_preview.pdf[/url] eehh may have jumped the gun a bit on that one, think I meant ACI 350.

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[Agent666]

How high is the wall so I can compare with my own experiences?

 

[Buleeek]

Agent666,

Total wall depth = +-6.5'
Pool depth varies= 3.5ft - 5.0ft
4,000psi concrete

Thanks,

 

[Agent666]

Round these parts for residential pools for comparison you'd see 150mm (~6") wall with 12mm (slightly smaller than #4) at 150mm (6") centers for roughly similar height. Bottom intersection of the floor amd walls always has a 300mm (12") radius to it. Almost always limited by crack control criteria, early age thermal cracking, limiting bar stresses, etc. Ultimate capacity never governs. All the checks are serviceability based, for simplicity unless you already have design spreadsheets and the like setup for 2 layers, just ignore the compression bars as it's going to be conservative.

If you were going thicker and to two layers you'd look at spreading the reinforcing out a bit no doubt provided you still meet all the crack control requirements (I've never done one that thick, but you may find whatever water retaining code you are working to may have a spacing limitation to control the crack widths midway between the bars). Sometimes in these water retaining codes there is a benifit to water retaining properties if the compression block depth is greater than some finite depth, but this is probably more applicable to more serious water retaining structures rather than residential pools!

 

[OldBldgGuy]

In my experience (mostly cisterns, but a few pools) closely spaced small bars are desirable for crack control (10M @ 8" for example) and they almost inevitably exceed what you need for strength. Just remember, a very strong and solid sieve is not much use as a pool.

 

[Tomfh]

In Australia a common design is 150 thick with central layer of S12 bars (softer grade bars that can be easily curved to suit the pool form). This is for pools with 1800 (6 foot) deep end.

If you were going to 10" I would go to 2 layers.

Make sure you have enough cover. Due to the curving geometry it often hard to get exact cover, and where the cover is insufficient the pool will rust and spall in time. I am currently repairing my pool, which is a 40 year old 150 thick shell, with S12-300 bars. The documented cover is 60mm to the water. It has rust spots in a half dozen locations where the cover is less than 60mm.

s12-300 is fairly light reinforcement, but this pool is functioning ok. It's 13 meters long, and has a couple of transverse hairline cracks. They don't leak. I'll be waterproofing over these prior to resurfacing.

 

[hokie66]

Not sure everyone is talking about the same problem. Buleeek called it a "free standing" pool, and the other comments are about an in ground pool, probably shotcreted. Also not sure what Buleeek means by the "outside" face.

Just a bit of clarity needed.

 

[Tomfh]

other comments are about an in ground pool,

I was talking about general shotcreted concrete pools, which can be in ground or out of ground. Our pool for example is in ground on one side, and above ground on the other side.

 

[hokie66]

Sure. The OP's talk of 8" or 10" walls and no load other than water, led me to think formed walls, all above ground. But that does sounds like a strange pool arrangement.