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.

"Danny Monaghan" wrote:
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.

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

I fear it may be time to consult a structural engineer.

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.

"Danny Monaghan" wrote in message
...
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.

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

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?

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.

"Christian McArdle" wrote in
t:

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.


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.

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


Which was why I sought further advice

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.

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.

"Christian McArdle" wrote in
t:


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.



Ah! Thanks for the that Christian

"Danny Monaghan" wrote in message
...
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.
...
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.

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

In article , Danny Monaghan wrote:
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?

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.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.10 released 4 April 2005]

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.


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

"nick smith" wrote in message
...

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.

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)

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.

"Mike" wrote in message
...

"nick smith" wrote in message
...

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.

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)

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.

I've been to parties like that.

Colin Bignell

"nightjar .uk.com" nightjar@insert my surname here wrote in message
...

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.

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)

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.

I've been to parties like that.

Colin Bignell

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

Tony Bryer wrote in
:

In article , Danny Monaghan wrote:
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?

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.


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?

In article , Danny Monaghan wrote:
although he did add that people standing in the pool presents a
point load that needs to be considered as well.

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

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.10 released 4 April 2005]

although he did add that people standing in the pool presents a
point load that needs to be considered as well.

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

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.

"Christian McArdle" wrote in
t:


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.


Unless it's the final straw

I think, all things considered, that I'm going to opt for cutting and
filling a level base. This will require little in the way of retaining
structure, and will probably take no longer to build. It will also save
quite a few hundred pounds (sterling, not weight )

It's not going to give me the desired finish, but it's a compromise I'm
happy with.

Now I've got to get digging because the pool has just arrived today.

"Tony Bryer" wrote in message
...
In article , Danny Monaghan wrote:
although he did add that people standing in the pool presents a
point load that needs to be considered as well.

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


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

Regards Jeff

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

Or swimming rather than drowning :-)

Owain

Danny Monaghan wrote:
Tony Bryer wrote in
:

In article , Danny Monaghan wrote:
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?

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.


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

same here.....

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,

Same here again :-)

but basically he says that my
original design will do the job

Likewise, with max 6ft spans, see below.

- 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?

A bit late replying to this, you have probably started digging out by
now, but anyway, this is based on a five minute conversation with my
husband over a cup of tea .....

Yes, you could use 6 x 2 s for this sort of load over a span of 'about 6
feet'. However, he says that although it could be done in timber, as
long as you had a solid base, block walls etc, used the shorter lengths
of structural grade pressure treated timber, it still wouldn't be a long
term structure. Wasn't keen on the OSB/bitumen (I think that's what you
said, my other newsreader has 'gone wrong', I'm back to OE and haven't
got your original post atm) at all, wouldn't stand the water, would rot
quickly.

Suggests the best way is to dig out as others have mentioned. However,
it could aslo be done using those pre cast concrete beams into which pre
cast concrete slabs sit. This could provide the base for the pool and
you could build the decking around the edge. If you haven't started and
still want the pool raised, you could look into this idea.

Our plumber is in the process of putting in a pool like yours in a
similar situation. After a similar conversation he has dug out the base
so that the pool is level with the ground at the top of the slope, and
he is going to build the decking up to the same level at the bottom of
the slope.

We are being much more conventional and are soon about to start digging
a bloody great hole :-)

HTH
--
Holly, in France
Holiday Home in Dordogne
http://la-plaine.chez.tiscali.fr/

"Danny Monaghan" wrote in message
...
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.

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.

"Danny Monaghan" wrote in message
...
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.


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