Above ground pool design

[XR250]

I have a good customer who wants me to design an above ground concrete swimming pool. I generally shy away from these things but he can’t find anyone else to do it. It is 14 feet wide by 30 feet long with 6 foot tall walls. He wants to use the pool bottom as the footing for the pool walls. Is there much to designing these things? Just design it as cantilevered retaining walls with 6 feet of 65 PCF per foot pressure? Throw in 0.6% Ag for shrinkage and in the corners and call it a day? There’s plenty of money in this job so few hundred dollars of extra rebar is it gonna hurt anything. Any other detailing I should consider? Should I put a keyway at the base of the wall? He will have a pool company waterproof it for him.

Thanks

 

[LowLax]

Why would someone want an above ground pool made of concrete? Seems expensive, but maybe this is a high-end specialty thing. Above ground pools are usually made from galvanized metal walls/posts and a plastic liner.

If it has to be concrete I'd probably do a waterstop at wall/base cold-joint, maybe waterproofing admixture, maybe galvanized or epoxy coated bar. Salt water or chlorine pool might effect corrosion. I think all the risk is in the possibility of leaks. What happens when the concrete cracks? (it probably will) I'd request a meeting with the waterproofer to see if they have concrete finish requirements. Consider the weight of the pool and potentially settling into the ground unevenly. If you're in a cold climate frost heave could be a concern. Subgrade prep seems important so might want a geotech consult. For concrete walls I usually do 0.0012Ag vert and 0.0020Ag horiz minimum. 0.0018 for slabs.

Otherwise the analysis part is pretty simple. I'd make sure it's plenty strong full or empty.

 

[Tomfh]

Pool detailing has a certain style about it.
Find some existing swimming pool drawings to get an idea.

Standard designs in Australia are in the order of 150 thick with S12-200 steel central, shotcreted. The S grade allows them to site bend to form the curves.

 

[hokie66]

XR250,

You are on the right track with the 0.6% Ag. You need to consider how the corners are rounded. LowLax is correct about the subgrade and possible frost heave. Suggest you consult with a pool builder about how they would build it.

 

[JoshPlumSE]

Why would someone want an above ground pool made of concrete? Seems expensive, but maybe this is a high-end specialty thing. Above ground pools are usually made from galvanized metal walls/posts and a plastic liner.

I had a friend who specialized in pool design for a number of years. He did an insane amount of volume. Like hundreds of different projects month. Most were in the ground. Those are easy. It's just a retaining wall design with the worst case being the pool being empty and some assumptions about footing length and ignoring the curvature of the pool.

Above ground isn't all that uncommon for "high end" jobs. Think hill sides with a 'vanishing edge' pool. They look crazy cool and make the view look even better. These aren't a whole lot different. Usually they're partially embedded in the ground. But, not always.

I help him with one project where the vanishing edge was next to a 100ft drop and there was a neighbor's how at the bottom of the drop. For this project the AHJ was really particular and wanted us to do a "sloshing" analysis like you'd do for a water tank. So, we did. It was a little trick because of the varying depth of the pool. But, we did a good enough job to get the project built. It was crazy expensive with deep piles and very much over designed. But, the client didn't care about construction costs. He was rich and he promised his wife he'd get it done for her.

 

[XR250]

You need to consider how the corners are rounded

Do the corners need to be rounded? I assume sharp corners would be more prone to leaking? The contractor wants to form this up with plywood or aluminum and pump it.
Thanks for everyone's advice.

 

[MotorCity]

I would also use waterstops (preferably self expanding bentonite) at wall to slab joint and throw in some Xypex for an extra measure.

 

[hokie66]

Corners don't have to be rounded, but domestic pools usually are not just rectangular boxes. The rounding helps with protecting opening corners. If you use square corners, use U-bars instead of just hooks.

In my opinion, Xypex is snake oil, so no need for that.

If the concrete box is to be waterproofed by a reputable pool company, some of the concerns go away. But what finish will the pool have?

 

[XR250]

If you use square corners, use U-bars instead of just hooks.

Not sure I understand what you mean? I was going to put corner bars in that lapped the horizontal reinforcing.
The contractor wants to make a rectangular box FWIW.

 

[gte447f]

XR250, I think I would approach this as a rectangular concrete tank and design per the PCA Rectangular Concrete Tanks design manual. I would also use ACI 350 for Environmental Engineering Concrete Structures. Water stops, extra rebar for crack control, tighter concrete specifications, etc.

 

[Tomfh]

Are they going to waterproof it? Concrete pools are typically not waterproofed. It can be done, but introduces its own set of problems.

 

[Brad805]

We have done a few of these in Hotels with small pools and hot tubs. We typically have a specialty supplier that deals with all the mech/pool requirements. We normally have a non-slip surface over the concrete and they have all the various corners needed to comply with the local pool regs. I am not sure how it is done in the residential world. We detail the concrete to be watertight (crack width < 0.3mm) assuming no membrane.

 

[hokie66]

Tomfh, that may apply to inground pools, but this is above ground.

XR250,
Hairpins in both directions. Work by Arthur Nilson and others has shown that corner bars do not make for efficient load transfer. The below thread is one of many on this site where this has been discussed.

https://www.eng-tips.com/viewthread.cfm?qid=479389

 

[Tomfh]

Hokie66, I am referring to above ground concrete too. My concrete pool is mainly above ground and no membrane. Same as my previous pool. Same as all my neighbours pools.

 

[ggcdn]

This ACI code provides a methodology for calculating hydrodynamic loads, if you are in a high seismic area. AHJ in California often ask for it to be checked.

https://www.concrete.org/store/prod...CTED_PDF&Language=English&Units=US_AND_METRIC

-JA
try [link calcs.app]Calcs.app[/url] and let me know what you think

 

[XR250]

thanks sonofatkins. I'm in a relatively low seismic area so it should not be a huge problem.

 

[ATSE]

Seismic or no seismic, there are still non-trivial hydrodynamic pressures in a swimming pool.
Especially when Fat Albert does a belly flop. Those pressures are more than just waves at the surface.
Don't underestimate these dynamic loads, and treat the pool like a chlorine contact basin (ACI 350, highly corrosive).
hokie: agree with U bars at corners instead of hooks. Better connection, lower congestion.
hokie: disagree about Xypex. Might be oversold at times, but it is definitely more than a placebo, and I've had several clients require it based on their very positive 30+ years of experience with their tanks.

 

[Tomfh]

non-trivial hydrodynamic pressures in a swimming pool.
Especially when Fat Albert does a belly flop

Do you have any references for that?

 

[la belle vie]

Consider using galvanized or epoxy coated rebar since there will be chlorine. Can you convince your client to use a liner? Without one the outside of the pool could start looking really ugly as water finds its way into cold joints and hairline cracks.

 

[ATSE]

An upper bound solution to the near instantaneous hydrodynamic pressures via fundamental force definition:
[vertical momentum of Fat Albert / contact area at top of water surface] / [delta T], where delta T is 0.1 second.
The pressure diagram is assumed as horizontal acting rectangle.
Again, upper bound. The actual pressure diagram is of course very complex.
My friend got his PhD in mechanical engineering, with CFD emphasis, and he confirmed this was defensible and reasonable.
These pressures are added linearly via superposition to the hydrostatic pressures. The final result will be on the order of 2x hydrostatic. For LRFD / strength design, I would use a lower load factor (1.2), because this pressure is close to "ultimate."