Need a Structural Engineer - Concrete Wall

[Pooh_Bear]

I want to build an above ground square concrete tank.
24 feet x 24 feet filled with water 5 feet deep.
I want to pour a slab and build walls on the slab.
How thick should the slab be. And what about reinforcement.
I realize that I would probably be better off to erect
forms and pour the walls as a monolithic casting.
But I have a different idea for the walls.
Concrete block walls using 8 inch block to form the interior wall.
Then another exterior wall with a space between the two walls.
The blocks would be filled with concrete and the space
would also be filled with concrete. All pinned to the slab.
How wide should the space between the walls be.

I saw this same design in a book about 30 years ago.
It was for an inground swimming pool.
And the space between walls was 4 inches.
But I want to build it above ground.
And I need to know how thick the space should be.

I can't seem to find an above ground pool
that is at least 5 feet deep. So I will build one.

Thanks for any and all advice.
You're also welcome to tell me I have fluff for brains.
But I already know that part.

Pooh Bear

 

[6sunset6]

Can't answer your question but I had sort of the same problem. My wife does water aerobics all the time and we were thinking about a pool kind of thing but no where could we find one the right depth which was around 5'.
We since dropped it cause it's her social time with the other ladies.

 

[Pooh_Bear]

That's what I am wanting it for, water aerobics.
There's a couple of places over in Chattanooga I could go.
But it costs almost $15 in gas to drive there and back.
I could get a season pass for the pool here but they are
only open when school is out and then only till 4pm every day.
I have been wanting a pool anyway. So this seems like the best way to go.

Pooh Bear

 

[CurlyDave]

Seems to me that is going to be very thick-walled when you count the double layer of 8 inch block and the fill in between. Expensive too. And, I am not convinced you will be able to get a watertight joint between the concrete pad and the block. The fill won't help a lot there either, since the area between the block walls is going to collect a lot of debris before you get a chance to pour it. Plus it will be a cold joint.

Now, with all that out of the way, the design of the pad and how the vertical rebar in the outer block wall is designed will have a lot to do with the ultimate strength of such a pool. Just pinning the vertical bar to the pad is not good enough. You need to have an engineer's design, and I bet it includes L-shaped bars with one leg in the pad.

The design is more than possible. I am not a registered engineer, so I can't design a structure for you, but I am an engineer, and I have designed many retaining walls for myself. The requirements for a retaining wall are higher than those for a swimming pool. The earth behind a retaining wall is presumed to act like a fluid with a density of 100 pounds/cubic foot. Water has a density of 62.4 pounds per cubic foot.

If you were willing to pour the walls I bet you could get by with 6" thickness, 8" for sure.

Of course you are going to need a deck around this pool so there is a graceful way to get out. Attachment points for the deck structure should be set into the concrete if you pour it, which will save you a fair amount of cost on the deck.

 

[jklingel]

Bear: My biggest concern would be the "soil" compacting and footer work necessary. Your water will only weigh about 311 lbs/sqr ft, which does not impress me as being great. (I AM NOT AN ENGINEER.) I've driven a one-ton truck and into my garage (4" slab, only wire mesh) for 30 yrs, and that sure gives more than a 311 lb/sqr foot load. For two years, I've also driven in a 6100 lb loader. On my son's basement walls, we poured 12" foam blocks full (8" inside) w/ rebar reinforcement. Horizontally, every 2' had two, #4 rebar. Vertically, every 2' had one #4. The slab, poured first, had 24" of #4 rebar protruding every 16" into the wall. (This was info as per the foam block guy; standard procedure.) I'd BET that your water will exert no more force than what a basement is designed for; wet dirt, fuel trucks nearby, etc. Have you asked a concrete place? Surely they can advise at least about the floor, and I bet a 5" slab w/ mesh and rebar criss-crossed on 2' centers is gross overkill. What they say to do, do more; it is cheap.Good luck. j

 

[MrJimi]

PB, just dig a hole in the ground and be done with it or put an above ground pool in the ground, I think Timber did that?

 

[MikeD74T]

On a well compacted area pour a 5" slab reinforced w/wire mesh, footing pins, & use dumbell waterstop White Cap Construction Supply - GREENSTREAK, INC - 4"X3/16" DUMBELL WATERSTOP 50'/RLL (prod# 483GS741) 4" in from the edge. Get a foundation contractor to pour 8" walls. If you want a supersmooth finish get a custom made vinyl pool liner & skip the waterstop. Cover the walls w/poly & keep wet for 30 days. MikeD74t

 

[Red55]

Mike-
You beat me to it but that was what I was going to recommend for the water seepage between wall and floor. Didn't realize how expensive it was. Would also recommend an above ground pool. The engineering is already done for you and the cost and maintence of concrete is getting to be out of this world. Know you want 5' and have seen a lot of models at 52" maybe an optional 5' liner is available. -Ed

 

[Egon]

I think I'd go for a monolithic pour walls and floor at the same time.

What is the reasoning behind the double block walls??

 

[Pooh_Bear]

Wow, thanks for all the great info.

The double walls create the form for the monolithic pour.
Supposed to be a poor man's way to build a pool.
At least that was the design I saw back in 1977.

I saw this design for an inground pool in a book when I was 10 years old.
My Dad built an inground pool based on the design but he didn't use a
second wall of concrete blocks or the fill space between walls. He used
one wall of concrete blocks and went just over 5 feet on the shallow end
and just over 6 feet on the deep end. And didn't fill the centers of the
blocks. We couldn't fill it up all the way but we had fun in it for many years.
The new owners of that house had the pool filled in with a dozer.

I want to do an above ground version to match the height of our back deck.
My version will be the same depth all around. If I could find an above
ground pool that is the right depth I would do that instead.

Pooh Bear

 

[crashz]

The concrete blocks and floor sound knida rough on water-softened feet and hands. Scraps and chlorine = Ouch!

BTW - I've seen a bunch of threads lately asking for help from engineers. I'm not sure if many people know this, but engineers carry a great deal of liability when we make a recommendation or suggestion. We are going through this at work where casual observations and comments have turned into litigation and loss of licensure. Sounds nit picky, but on the otherhand, it causes engineers to see through an entire project if their name is on it. Also it clearly defines "stamping" of plans as illegal unless under direct supervision.

I'm not trying to rain on anyones parade, but I am trying to explain why most licensed engineers will not pipe up and start recommending things to people.

 

[Shmudda]

Look into a prefabricated concrete tank like a cistern. There are companies out there that specialize in that sort of construction and it will be cheaper in the long run.

Craig

 

[Pooh_Bear]

You are right. Perhaps I worded it wrong.

I am building a concrete container.
I need a structural engineer familiar with such construction,
and I very well may consult with a PE before I start.
But for now, I'd like opinions from the smart folks we have here.
Some of them may even be engineers. I value all opinions.

I am thinking a minimum of a 1 foot wall between two 8 inch block walls.
Fill the blocks with concrete and anchor it all to the slab.
Use lots of rebar and concrete wire. What do y'all think.

Pooh Bear

 

[JiminGa]

what about just finding a 12 ft or so diameter pipe and setting it on end, then poor the floor and line the whole thing?

 

[Egon]

Your idea will work Pooh.

It may even be overkill!

 

[tommu56]

Pooh_Bear
Any old silo's around your area?

I looked at one for a water tank but couldent come up with a good way to hall all the blocks and rings.

I'm sure they can be rearrainged to a larger diamater from a smaller one.

tom

 

[tommu56]

Pooh_Bear

this might work

Ferro - cement tank


tom

 

[MikeD74T]

tommu56's idea will definitely work. During my masonry apprenticeship I helped plaster two ferro cement sailboats. These were 40' boats. 6 plasterers & 4 tenders working start to finish. When cured they would ring like a bell if struck with a 2x4. The owner gave me a book, which I loaned & never got back, that described the process. The most critical part was the ratio of steel to concrete. MikeD74T

 

[Egon]

The ferro cement will work but is very steel intensive.

Back about 40 years or so there was a surge in ferro cement boats as it looked cheap and simple to build. It's very labour intensive and does require consistency during construction. Mistakes are not easily covered. As people found the amount of labour and quality required they fell out of favor. These type of boats have been around for many many years.

Another poster may recall a post in which he mentions the number for sail in Hawaii after the first crossing!

 

[zeuspaul]

I am not a structural engineer.

The floor of the tank should rest on well compacted good base material. Rebar isn't as important here as it is on the sides.

As you indicated the block acts as a form for the poured pool. You're going to need a lot of rebar in the vertical walls. There is nothing *pushing back* on the walls as there is on the floor. You need more rebar towards the bottom as this is where your greatest force is. I would use 20 ft rebar and a lot of overlap. Consider channel block to hold the rebar (horizontal and vertical rebar) Then fill the block with concrete.

You need a good joint where wall meets floor. Consider ell shaped rebar. I would size the thickness of the slab for good rebar coverage at the floor. A six inch slab would give over two inches of coverage for the rebar.

Dry stacking the block might be an option if the arcs are smooth enough. Quickrete makes a product Quickwall which is used for dry stack block. It has a smooth finish and is supposed to be water proof (not necessay with inner poured wall) They also make a product to assist in waterproofing the floor joint.