Above Ground Swimming Pool Deck Structure

[Danny Monaghan]

Just about to take delivery of an Intex 15' diameter above ground pool - one of the metal frame and liner type. As the garden slopes, I need to create a level decking to sit the pool on.

The plan is to build a 16' x 16' deck from joists and bitumen coated OSB. the pool will sit on this and round the pool decking planks will be laid to give a finish to walk on. 95% of the deck will be under the pool. The slope of the garden means one end will be at ground level, raising to about 18" at the other end. The whole structure will be supported by block pillars (apart from the the end at ground level which will sit on the ground via concrete flags) and 4 cross joists.

An ASCII art diagram may help the picture (X are block pillars):

|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | X-|-|-|-|-X-|-|-|-|-X-|-|-|-|-X | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | X-|-|-|-|-X-|-|-|-|-X-|-|-|-|-X | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | X-|-|-|-|-X-|-|-|-|-X-|-|-|-|-X

The question is, to cope with the massive weight of water, should I use

6" x 2" joists at 12" centres, or will smaller timbers and/or larger centres be okay - or a combination of sizes? Also, will a single layer of 16mm OSB me sufficient for the deck surface, or would this be better thicker?

Access to the garden, and time are the main reasons why this has to be built like this, rather than building retaining walls and filling with soil.

Any comments and feedback would be great thanks.

[Al Reynolds]

I fear it may be time to consult a structural engineer. I wouldn't even consider putting a pool of that size on a deck, but then I'm not a structural engineer. Think about the consequences if the deck collapses and someone/something is on the wrong side of it.

Al

[Baz]

For every meter of depth of water in your pool you will have 16 tonnes. Like Al suggested, consult a structural engineer. Baz

[Aidan]

If it's 42" deep, I make the weight of water to be about 17.5 tons. If you put it on the deck, I recommend not filling it.

[Christian McArdle]

I haven't played with Superbeam for some time. Don't you dare construct this without getting full calculations from a structural engineer. My Superbeam skills are very rusty and I've probably made a heinous mistake.

Assuming 1.5m depth of water in the pool and 300mm joist spacing, I make these

50x170 C16 timber joists.

The cross beams I calculate to be impossible to make in wood using your design. Using steel, it comes up with a 127x76x13 Universal Beam as a solution.

Alternatively, having 7 pillars supporting each cross beam, and having 7 cross beams, instead of 4, I make 50x195 C16 timber beams, with 0.8m between beams and 0.8m between beam supports.

Remember, I'm not a structural engineer, I've made loads of assumptions, can barely remember how to use Superbeam and I'm probably talking out of my arse!

Note that you're unlikely to be able to construct foundations for the columns without serious hardware and calculation. Using the 7 beam/support solution, each column (in the middle) is carrying about 1 tonne. With a 4 beam/support (steel) solution is carrying almost 4 tonnes.

Basically, this isn't a case of getting a few bits from B&Q to put a paddling pool on.

Christian.

[nightjar]

...

I doubt you will save any time over putting in the sort of foundations you are likely to need. I wouldn't be too happy with the retaining wall and fill solution either. To my mind, the way to do this safely is to excavate the garden to create a flat terrace in the slope.

Colin Bignell

[Tony Bryer]

I agree with the others that this needs an engineer's design. Domestic floor are designed for an imposed load of 1.5kN/m2 (30lb/ft2); you've got 1.05m of water = 10.3kN/m2 (218lb/ft2) - 7 times the load. Apart from the structural side I'd be concerned about splashed water getting trapped between the underside of the pool liner and deck surface.

[nick smith]

Hi Tony,

Does this mean when I stand with my feet together the floor is over loaded ?

I weigh about 180 lbs and both my feet would fit within a square foot, if you'll pardon the pun (not intended)

Nick

[Mike]

No you don't. For this sort of weight you need to dig and then pour proper concrete foundations. Re-inforcing them with steel might also be needed depending on the slope and soil composition. Get a structural engineer round ASAP.

[Mike]

No because you are a single point load. But if you put one of you in every square foot the floor would indeed be overloaded.

[nightjar]

I've been to parties like that.

Colin Bignell

[Mike]

"nightjar .uk.com>" >>

Yeah. Seem to recall BBC news showing a balcony collapsing at a party some years ago which sort of proves the point.

[Rick Hughes]

What you should consider is making the pool free standing .. then have the deck free standing around it, then the load on the deck is just you + sunloungers .... crazy to try and hold up the pool this way.

Rick

[Danny Monaghan]

"Christian McArdle" wrote in news:4291fb20$0$302$ [e-mail]:

Thanks for the replies to everyone.

What I can't work out with your calcs above (and forgive my ignorance on engineering loads) is how a 16 tonne load becomes 4 tonnes per pillar - surely spreading the load reduces the overall load. This seems to add up to

48 tonnes? This does show my complete lack of knowledge on this subject.

Which was why I sought further advice :)

[Danny Monaghan]

Tony Bryer wrote in news: [e-mail]:

What span does that imposed load apply to? Does a shorter span on the same timbers push the load capacity up?

I've just finished speaking to an engineer and he came up with the same

10kN/m load you've calculated, but he said to me that's light (I actually laughed when he said that). This was quick musings/scribblings, not a full quote, but basically he says that my original design will do the job - although he did add that people standing in the pool presents a point load that needs to be considered as well. The height of the pillars is low enough to not worry about then slewing.

He also suggested cutting and filling (because of the lack of access for bulk products) may be a another solution. This would leave a smaller retaining wall which would not be a problem for the load.

Any more thoughts please?

[Christian McArdle]

It is calculated on the centre pillars, which are loaded above average. I also assumed 1.5m depth, giving a total water mass of about 24 tonnes. The edge pillars will have only a small fraction of the worst case load.

Christian.

[Danny Monaghan]

"Christian McArdle" wrote in news:4292fb4a$0$303$ [e-mail]:

Ah! Thanks for the that Christian :)

[Tony Bryer]

Does it? 100kg of person displaces 100kg of water - i.e. the water level rises fractionally across the whole pool leaving the loading under the person more or less unchanged. Or so ISTM

[Christian McArdle]

There's a point load if you stand on the bottom. It is the mass of the person minus the amount they happen to be displacing. This is approximately equivalent to the mass of the body parts above the water level (and exactly so if the human density==1). However, with a 1.5m level, this difference (and hence point load) is likely to be small.

When swimming, they will displace their entire mass, leaving no point load.

In any case, the additional weight is peanuts.

Christian.

[Jeff]

That presumes that the person is floating rather than standing ;-)

Regards Jeff