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Area of a circle?
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tahir



Joined: 28 Oct 2004
Posts: 43954
Location: Essex
PostPosted: Thu May 11, 06 9:54 am    Post subject: Area of a circle?  Reply with quote    

What's the area of a circle with a 3.66mtr diameter?

This is going back to my water problem:

My 16 tonne water tank (3.66m) is going to sit on a concrete base of indeterminate strength and depth, I've been advised by monkey1973 to put another 5" reinforced slab on top, I reckon this will be 14" at the deepest (due to slope) so it's going to be a heck of a lot of concrete, several tonnes I reckon. Wouldn''t the weight of the slab affect the underlying slab? And how much extra area will the load be spread over by doing this?

i.e. Is it worth it? Rich the tractor says he'd probably make a level sand and cement base and lay the tank on top of that.

Any ideas anyone?

Northern_Lad



Joined: 13 Dec 2004
Posts: 14210
Location: Somewhere
PostPosted: Thu May 11, 06 9:57 am    Post subject: Reply with quote    

Pi x radius squared

Bernie66



Joined: 14 Jan 2005
Posts: 13967
Location: Eastoft
PostPosted: Thu May 11, 06 9:57 am    Post subject: Reply with quote    

Area of circle is pi r squared. so 3.66 diameter is 1.83 radius. 3.14159265 times 1.83 squared is 10.52 meters square. somebody check my maths!!

tahir



Joined: 28 Oct 2004
Posts: 43954
Location: Essex
PostPosted: Thu May 11, 06 9:58 am    Post subject: Reply with quote    

What's Pi? (Haven't had much cause to use it in the 25 years since I left school)

Bernie66



Joined: 14 Jan 2005
Posts: 13967
Location: Eastoft
PostPosted: Thu May 11, 06 9:58 am    Post subject: Reply with quote    

Got the same answer twice so i reckon its right

Bernie66



Joined: 14 Jan 2005
Posts: 13967
Location: Eastoft
PostPosted: Thu May 11, 06 10:00 am    Post subject: Reply with quote    

tahir wrote:
What's Pi? (Haven't had much cause to use it in the 25 years since I left school)



I only use pi and pythagoras now from most of the maths I used in school. other than basic add subtract multiply divide etc.

Nick



Joined: 02 Nov 2004
Posts: 33696
Location: Hereford
PostPosted: Thu May 11, 06 10:01 am    Post subject: Reply with quote    

You can treat Pi as 3.14 for most applications.

Bernie66



Joined: 14 Jan 2005
Posts: 13967
Location: Eastoft
PostPosted: Thu May 11, 06 10:05 am    Post subject: Reply with quote    

http://3.141592653589793238462643383279502884197169399375105820974944592.com/

Or...............

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Thu May 11, 06 10:06 am    Post subject: Reply with quote    

pi r squared.

Diameter (d) = 3.66m divided by 2 to give radius (r) =1.83m

1.83m squared (1.83 x 1.83) is 3.3489.

3.3489 times the magic number (pi) (3.1415926.... goes on forever) is 10.520879 square meters, which is ridiculous, or 10.521 square meters.

So my sums give the same answer as Bernie66.

Tahir, sooner or later, when your bairns start asking for help with their homework, you'll have to learn all this

Last edited by cab on Thu May 11, 06 10:08 am; edited 1 time in total

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Thu May 11, 06 10:08 am    Post subject: Reply with quote    

nickhowe wrote:
You can treat Pi as 3.14 for most applications.


Or, like me, you can just use whatever number your calculator says it is, and it'll remember more decimal places than I ever will. Lazy, I know...

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Thu May 11, 06 10:11 am    Post subject: Re: Area of a circle? Reply with quote    

tahir wrote:
This is going back to my water problem:
My 16 tonne water tank ...


Previously, the tank was to hold something like 24 tonnes of water.
So is this thing 16 tonnes empty? Or a smaller tank?

I can't help but think that some recycled IBC's would be both adequate and cheaper. What's this sort of tankage cost, before the foundation work?

tahir



Joined: 28 Oct 2004
Posts: 43954
Location: Essex
PostPosted: Thu May 11, 06 10:15 am    Post subject: Reply with quote    

Bernie66 wrote:
10.52 meters square.


OK the slab will be 6x5 so 30 m2. I suppose thats a significantly greater area to spread it over. So should be a useful increase eh?

tahir



Joined: 28 Oct 2004
Posts: 43954
Location: Essex
PostPosted: Thu May 11, 06 10:18 am    Post subject: Re: Area of a circle? Reply with quote    

dougal wrote:
So is this thing 16 tonnes empty? Or a smaller tank?


A smaller tank, it's 800. We've gone large as the system needs to be expandable.

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Thu May 11, 06 10:37 am    Post subject: Reply with quote    

tahir wrote:
Bernie66 wrote:
10.52 meters square.

OK the slab will be 6x5 so 30 m2. I suppose thats a significantly greater area to spread it over. So should be a useful increase eh?


Again - I know little about 'Civils', BUT

to spread the weight of the tank, you are relying on the *stiffness* of the new slab, which is going to be limited by (if you think abouut the way the slab is going to be bent) the maximum tension that the underside can take.
Concrete is rubbish in tension.
Thats why its often reinforced.
Incorporating some steel bar/mesh should allow the slab to be thinner than if it was unreinforced. (It'd be even better if you could pre-tension the reinforcement, but that's not AFAIK at all easy...)


800 - well if you could find 20 1tonne (1m cube) IBC's @ 40 each in quantity ...

tahir



Joined: 28 Oct 2004
Posts: 43954
Location: Essex
PostPosted: Thu May 11, 06 10:39 am    Post subject: Reply with quote    

dougal wrote:
you could find 20 1tonne (1m cube) IBC's @ 40 each in quantity ...


But then you'd have to link em all up.

Just had another thought. what if we break up the old slab and use that as a base for the new? It'd be more expensive but then it'd be a more "proper" job wouldn't it?

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