Elevated pool deep end infill options

[Jc67roch]

I am looking at a project to "infill" the deep end of a roughly 45 foot long by 25 foot wide pool. The pool is on the fourth floor (open plaza/courtyard deck) of a hotel, and is constructed of aluminum reinforced with structural ribs. The aluminum is also the interior pool surface - it just painted. It is drained, cleaned, and painted every other year. There is no liner. It is fully accessible below from the third floor mechanical space below. The pool is currently 5 feet deep in the shallow end, and tapers to 8 feet at the deep end. The hotel wishes to infill the deep end to 5 feet for cost purposes so that the lifeguards are not needed, there is less water to maintain, and liabilities are reduced. As the pool is elevated within the building, we are looking at options to keep the weight the same as the current filled pool or less for structural reasons. Our initial options being explored include:

1) fill the deep portion to 5 feet with geofoam and then lay in new aluminum plating on top (bearing uniformly on the geofoam, and thus existing pool below) and weld the plate edges to the existing aluminum pool - this would require some detailing of cement board, other thermal protection, or upturned flanges to prevent weld heat from melting the foam.

2) Filling the deep end with geofoam and installing a one-piece fiberglass pool inside the existing pool to roughly the same dimensions and grouting a small perimeter gap/clearance. This option would remove the bi-annual maintenance of painting the pool. But would require reconfiguring connections of scuppers, etc...

Other thoughts include use of lightweight concrete fill rather than geofoam - however I think the weight of even light weight concrete would be more than the existing water (62.4 pcf) possibly creating structural issues. Also, I think we should install a drain within the geofoam fill to capture any water or leaks that should develop - it could have a visible outlet as a "check" that there is no water leaking into the filled space.

Another engineering firm had suggested to the owner installing supporting aluminum or galvanized steel framing within the deep end to 5 feet and then the new aluminum plate over that. This would allow access within the old deep end. However I believe this would be more costly, create point loads where there is currently uniform water loads, and also require thicker aluminum plate in the new pool bottom to span between supports than using uniform geofoam fill.

Also, elevated height (on 4th floor - open roof deck) surrounded by higher hotel room building creates challenges with craning in the pieces for any work. We are thinking we need to helicopter skylift in any solution.

- has anyone done a project like this? Have thoughts or experience to share? Other ideas or options?

 

[hokie66]

Consulting with the original pool builder would be my first thought, as this type pool is normally proprietary.

 

[JAE]

With option 1 can you detail the geofoam to stop some distance from the welded areas and have the aluminum just span that short distance?

I would think that you'd only need about 18" or so to keep the heat down on the geofoam.

Also - keep in mind that welding aluminum changes the allowable stresses used in that material in the vicinity of the welds.

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[jayrod12]

What about building short cold-formed steel stud walls over the existing support lines and then installing a new liner. Essentially what the other engineering firm proposed. That way it's not point loads but line loads in the same locations they already exist.

 

[canwesteng]

Have you thought of using mostly geofoam with a drain, and then a topping layer of lighweight concrete? Use a concrete sealant and caulk the edges. Just spitballing, I haven't given this any serious though.

 

[calvinandhobbes10]

Elevated pool---leak risk reduction is important, although it sounds like they didn't put occupied spaces below.

Option 2 is most appealing except I'm not jazzed about grout/fiberglass covering the alumnimum bowl permanently. Seems like potential hidden issues with all those interfaces. I think you're best off keeping it alumninum, better cost also.

I'd go with overbuild cold-formed per jayrod instead of geofoam, since you're elevated. Your seam of new aluminum abutting existing is going to be your leak problem. I'm not sure if welding is best for water protection, or necessary structurally. I would want to count on a good seal strip, not welds, for watertightness. Belt and suspenders. A seasoned pool manufacturer is best bet to help advise for watertightness, I'm sure they run into the problem often.