maths question, need help please ..

signs

signs

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i need to fill a circular drain pipe with concrete and find out how heavy it will be .

the inside dimension of the pipe is 600mm in (edit ...diameter ) circumference x 250mm tall

any ideas please as my brain has gone into meltdown

cheers
 
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so what do we all know about wind load ?

going into the concrete base is a 2.5m x 76mm aluminium post with a 600mm x 600mm sign on top , how much battering will this take ?

Ta
 
Syla5 said:
This will be roughly 70.65 litre of concrete if I have got this about right.

Volume = pi * radius squared * height

= 3.14 * 300^2 * 250 = 70,650,000 cubic millimetres
= 70.65 litres

Concrete roughly weighs 2.41kg per litre, so 168kg+ the weight of the pipe.
= 2.41kg * 70.65 = 168.7kg
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this is about what i got it too also
 
adolf hamster said:
assuming a turbulent flow, maximum wind speed of 60mph (27m/s) for a good gale, density of air is in the region of 1.225kg/m^3 (google), and the plate being perpendicular to the wind direction (ie the worst possible force) giving a drag coeffecient of 1.28 (wikipedia)

then the drag force is going to be roughly:
e9582e0099f3d4ead6a6933118ed73bc99bd7cc6
(wiki)

=0.5*1.225*27^2*1.28*(0.6^2)=205N or the equivalent of the weight of a 20kg object

now the mechanics of will it tip come down to moments, or force*distance

so our wind force is creating a moment around the base and the top of the sign which is 205*2.5=514Nm

assuming the base doesn't slide along the ground and in fact tries to topple, pivoting around the edge of the cylinder then the moment it'll give is based on the radius of the cylinder and the force of mavity, in reality it's much more complex than that but this is as much detail as i can be bothered to give out for free on the internet but in this simplified version the mavity moment is mg*r=9.81*170kg*0.3=499.8Nm

now we could juggle this around, find out what wind speed would be needed to tip exactly (although we're not too far over with a 60mph gale), work out if the sign would slide along the ground or tip over, or even figure out if the aluminium pole would break before any of this happens, but that's all a pretty deep rabbit hole.
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brilliant , thanks , i've just commissioned an engineer to take a look (before reading this ) but i really do appreciate your response .
 
Jonnybmac said:
How much is burried and how much isn't? Where on the post is the sign pinned? Is the centre 300 down from the top or at the top?

Afaik you need to work out where the load is concentrated on the post to work out the max bending moment (would be found at the base) then compare that with the failure stress of the wood in that axis. You'd also need to work out an average force from wind pressure acting on the sign. Do you really need to do this?
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Hi Jonny

the sign is going to be set in a concrete base 475 mm diameter x 250mm height ( smaller pipe now but more robust ) the sign panel (600mm x 600mm) will be mounted at the top of the post (post 2.5m ) so 1.9m from floor level to bottom of sign.

so just trying to work out the "topple " factor

cheers
 
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update (just in case anyone else needs to do this !!!! ) i got a structural engineer report ... the concrete at the new smaller size weights around 13.5 stone and the sign "topple" is 50mph still standing at 70% of that

cheers all
 
AndyT said:
The sign will fall over in a 50mph gust, which is a Beaufort Scale Force 9 - (strong gale) - branches break off trees, shingles blown from roofs, high crested waves etc.

It might start rolling around / shifting slighty on its edge a little bit before that, but tha'll probably be reet.



EDIT:



Arrrgh, beaten to it. Never mind.
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wow that's impressive !!! thank you , make me wish i hadn't paid for the report now lol

I've gone back to the original size of base now 600mm x 280mm (ish) deep , any idea of the "topple" factor now please (if you have time that is ?)
 
AndyT said:
N
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it was a weird conversation with the engineer Andy , not used one before so i gave him the spec then he asked me how much i wanted to pay !!!! i said "you tell me" he said £150 , i said thats more than i wanted to pay ! he said how about £100? , i said how about £50 ? he said £75 . so i went with that
 
touch said:
You're not paying for the calculation, you're paying for his insurance.

If the sign blows over and damages something or someone and you can say that a qualified engineer told you it wouldn't blow over, he will be liable.
If the sign blows over and you say that a random person on the internet told you it would be fine, you're liable for the damages yourself.
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yeah fully appreciate that , the client was suitably impressed when i gave him the calculations yesterday , so it was money well spent in my view .
 
AndyT said:
Disclaimer:
Under no circumstances will AndyT be held responsible or liable in any way for any claims, damages, losses, expenses, costs or liabilities whatsoever (including, without limitation, any direct or indirect damages for loss of profits, business interruption or loss of information) resulting or arising directly or indirectly from your use of or inability to use the information freely provided or from your reliance on the information.
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i'm pinching that disclaimer !!!1:D
 
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