# Pool design

1. May 25, 2010

### Betenix

ok guys, suppose i wanted to build a round 8m diameter 1m high pool out of galvanized steel sheet. I will be filling it 0.7m with water.
I am aiming to reduce its cost so im calculating the thinnest sheet i am allowed to use without it failing.
I will be using 7 sheets bolted together(each is 1m x 3.6m).

The pressure at the bottom (P=p.g.h) came out as 6867 Pa. Now how do i work with this information? I am guessing a circular distributed force which acts on the 7 unions?

Any ideas?

Thankss

2. May 25, 2010

### xxChrisxx

It's not the strength of the material you need to be worried about, as even incedibly thin sheet will withhold that. The cost difference between gagues isn't that huge in the grand scheme of things. If it's a pool you don't want thin sheet metal as it will flex when people are in it.

It's your joints you need to be worried about. Unless it's fully welded, or you use some gasketing/bonding material it'll just leak all the water away.

This can be considered to be a cylindrical pressure vessel, with hoop stress being the largest stress. The size means we can assume it's a thin wall. Factor of safety of say 3. No ide awhat grade of steel you are using so i'll assume a yield of about 300MPa

Although if this is a pool, stainless would be a better idea.

stress = pr/t
(0.006867*8)/t = (stress yield/3)
0.054936/100=0.0055mm

So as you can see this is much much thinner than the thinnest sheet you can buy. Material strength is not the dominant factor in design here. It needs to be practical.

3. May 25, 2010

### cstoos

It is actually half that since you used the diameter instead of the radius.

4. May 25, 2010

### xxChrisxx

Oops! Well spotted.

5. May 25, 2010

### jrw66

Don't forget about the stress concentrations that will occur where you bolt the sheets together. Depending on how you are going to do to bolt the plates together, the stresses could get fairly high.

Also, depending on the grade of steel you buy, your failure mode may be crack propagation, not stress based failure.

6. May 25, 2010

### xxChrisxx

I'd agree with this, expecially if you try thing sheet steel, it will flex and likely tear at the jionts.

To be honest, steel is not the material i'd chose to make a pool from. It'd probably be cheaper to just get it made from a heavy plastic. If you have to go with steel, i'd go with a stainless rather than a galvanised steel. Or build a proper pool.