An in-ground pool with windows...Design Question: Stress limitations?

Factual Questions
1

I was working on a new design model for kicks and giggles and was wondering if there would be inherent stress problems with this:

I have a home in Arizona that has a Pool in the back yard. The pool comes directly up to the house almost attached…Picture walking out a back door and looking back at the house and the pool was attached lengthwise to the home. I thiknk the designer was looking for pool reflection to come into the home…not sure though. Anyway, unlike the typical Arizona home ours has a basement. The wall between the basement and the pool is roughly a foot thick cement foundation. Currently the basement is not used…except for laundry. If we were to finish the basement I’d love to have large windows in there showing directly into the pool. It would illuminate the basement with a really nice aqua blue color…and would be cool for parties and such. I know Aquariums have this set up…I was just wondering what kinds of stress implications we’d run into. The pool is rectangular 30 feet long by 12 foot wide. 10 feet deep at the rear and 3 1/2 at the front.

I’m wrestling with the idea because I am finishing my basement here in CT so obviously it got me thinking about our basement in AZ.

I’m thinking 2 inch plexy glass 5’ by 7’ pieces. Two of those side by side. I’d think it would look pretty neat. Would there be structural problems with the basement…if so what?

2

http://www.marvelglass.com/safetyglass.html
laminated safety glass

3

If you are removing structure from the basement, you’ll need something to span the window and carry the load (and I think you know this).

If it’s concrete, you likely have a lot of extra carrying capacity in those walls than is actually being used.

There are so many “ifs” that they’d be hard to get into. The easy part seems to be finding glass that will hold back the water and that can be incorporated into the design.

4

I’m a bridge engineer and I wouldn’t do this for anything. If your existing basement wall is retaining the water, it must have been designed to do so. There must be reinforcement on the side nearest the water that is being put into tension by the water bending the wall toward the basement. That reinforcement works because it is allowed to develop from a point of zero stress (top of wall) to maximum stress (base of wall). Now if you cut in a window, all of a sudden those bars are not going to function- they will need to be at zero stress at the top and bottom of your windows and the bars won’t have a chance to develop. I see real potential for failure, although without plans I could not compute it to be so. You’d be better off to have say 1’ wide windows so that you’re only cutting a few bars to get each in, and you’d want to space them several feet apart.

5

Thanks Bob - I’d be working with my brother-in-law who is a structural engineer, and I agree 100% that there are some big issues at stake here. I had not thought of windows with a smaller width…thats a good idea. Nothing is in the works yet, however, I may have him (BIL) draw up some preliminary plans to see about cost, materials, labor etc…etc…

Thanks for the glass link Phil, I sent it on to my BIL.

6

I’m very glad that you have qualified help. This is definitely a place that cries out “kids, don’t try this at home.” Most anything CAN be done, it’s just do you want to spend what it takes. You could always jack up the house, remove the basement wall, and rebuild it with windows in place. Then you could design the wall reinforcement to allow for the windows.

7

Phl I have got something that’d be perfect for what ya want. hmm…where’s that damned formula for making transparent aluminum at?

Aye cap’n there be whales here. :wink:
Sounds cool, an aquarium for the kids.

8

You mention the pool’s dimensions, but you didn’t mention which orientation the pool is in relative to the wall, nor the relative height difference between the basement floor, basement ceiling, pool floor, and pool surface.

In general, you can figure out the hydrostatic force in a situation like that using the following formulae:

F = PA (Force = pressure times area)
Pressure = rhog*y (Pressure = density * gravity * depth)

The integrals (if you want to do them yourself) are all here, but it looks like it simplifies to the following, for a rectangular area of width “w” and height “d” below the surface (with its top edge at the free surface):

Force = w * rho * g * d * d / 2, which in metric units simplifies to:
Force = w * (1000 kg / m^3) * (9.8 m/s^2) * d * d / 2
Force = 4900 * width * depth squared
{use meters for width and depth; result will be in Newtons}

If your window doesn’t go all the way up to the free surface, simply compute two rectangles: one that goes to the free surface from the bottom of the window, and one that goes to the free surface from the top of the window. Subtract the result to find the total (lateral only!) force from the weight of the water in the pool – this does not include shocks from people doing cannonballs, although those transient forces should be negligible unless you have a habit of detonating explosives underwater in your pool.

That said, I agree with BobLibDem: this is some serious pressure you’re dealing with, and the implications for the strength of the foundation are frightening. If you don’t really need to see the cover of Nirvana’s Nevermind from your basement, consider translucent glass bricks instead of one broad pressure-and-weight-bearing pane of glass or plexiglas.

If your heart is set on it, talk with the BIL (who probably knows this formula anyway!) about what sort of safety factor you want, and what sort of longevity you want out of your materials before selecting anything. Maybe call up Sea World or another large aquarium (like the Shedd in Chicago or the Nat’l Aquarium in B’more) and ask what they use for the two-story tall walk-around (or walk-through!) tanks?

9

BTW I totally agree w/ya safety first.

10

The email I just got back from my BIL:

[quote]

<snip>…Phil, you want to do what? Does my sister know about this yet? Just kidding, I’ll work out the specs this afternoon, and get back to you on the glass. Having three or four windows 1’ X 6’ would be much more practical and less stress on the wallet. Also, not sure about the code either, I’ll check and see what kind of permit we’d need, I now we’re going to need to tell the town about draining the pool…<snip>

[quote]

Thanks for the formula Jurph…I’ll write more in a bit…Time to head home…