Sandaysoft

Which begs the question then - why bother even putting it up if you aren't concerned about accuracy (general 'you' btw)

http://en.wikipedia.org/wiki/Fatigue_limit

And - again - putting up a 5 metre high pole of AMY type without guys is sheer stupidity.

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

I have it up to catch the hot air coming out of Victoria.

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Terry Wiltshire
http://www.janter.co.nz/weather/index.htm

This and a few other threads has got me thinking now
which pole would be best to go for, a square section or a circular
section, as well as what guage would be best to go for.

i.e. which is the best combination of section and wall thickness
would be best to resist wind movement.

Obviously a thicker guage would mean that it would
make the pole heavier, but would that make it sway in the wind
more or less? or would it make it more rigid and to be able to
prevent swaying?

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Cumulus Real Time Data Grabber
http://bit.ly/WjBh5z

Wokingham Berkshire - weather station
http://www.wokinghamweather.co.uk

MRD Photography
http://www.mrdphotography.co.uk

iirc wall thickness is largely irrelevant to stiffness, certainly for tubes it is the diameter that counts. Wall thickness of course matters for load bearing.

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Mark
Wilmslow Astro Weather

Mark, I would have to disagree if I understand the full meaning of the quote.

Randy

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Georgia Home Orchard

http://georgiahomeorchard.blogspot.com/

The wider the cross section of the pole, the more susceptible it is going to be to being affected by ANY wind - the longer the pole the more this effect will be noticed. That's why once you get to 3 metres or so you need to tie or guy the top of the pole to prevent this 'swaying' from happening.

Also - the longer the pole the stonger the mounting point also has to be because the force exerted on, say a 5 metre pole, is also going to increase. And keep in mind, even though an anemometer is designed to spin in the wind, it sits on a non-aerodymanicaaly shaped block which WILL catch the wind and exert another force on that pole - sure, small - but in the long run, it all adds up.

And to our 'kiwi friend' who thinks this is a load of hot air - maybe you need to dig out articles and photos of the wind vane at New Plymouth some years ago and have a look at the effect even a moderate breeze had on that (by design of course) - then you will see what can happen if not tied down properly.

Final thought - how many planning on putting up one of these have even thought to check with their local councils to see what they should do in terms of proper mounting and stabilising? Think a few will get a rude shock because if they don't check and it is later 'found' by a council, it could become a very expensive exercise.

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

It's been a long time since I had to do this stuff, but here goes -

The resistance to bending (and yes, ability to withstand load) on a beam or column is a function of the 2nd Moment of Inertia (I), and there are simple formulae to calculate it for different sections.
For the two square section 40mmm tubes of wall thicknesses 3.25 and 1.6mm, calculation shows I for the thinner section is 56% of the thicker one. For round 40mm O.D. tubes of same wall thickness, I is 59% of the square tube.
The actual deflections are also dependant on the Modulus of Elasticity of the material, and varies greatly between say steel and aluminium.

I wonder if the aerodynamic qualities of square section tubing (and the wind forces on it) would vary with the direction of wind onto the faces, just to complicate things...

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It's been a longgg time - but as you rotate the wind direction around a square 'tube' you increase the face (or cross sectional area) being presented to the wind even though there is also a slight decrease in the 'effect' because it is no longer square on to the wind.

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

Yes, wonder if they come close to cancelling out? Further, would 'I' for a square tube change if the load is not square on to a face?

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Not sure (about either - as I said - too long ago and no longer have books/notes ) but seem to recall they don;t exactly cancel each other, there is a slight increase because of the increase in surface area.

Maybe need a current engineer to do some calculations.

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

I have mine mounted the top of a 20' aluminum flag pole. No guy wires, it sways, no harm data runs very close to airport 2 miles away. Of course in a windy storm above 30 mph, I take the flag down and the sensors ride it out.

Out of interest then - is it sitting on top of the ground or embedded in concrete, sitting in a stirrup embedded in concrete? And, from the photo, appears to also be stayed to a post roughly 2 metres high? IOW - the base *appears* to be rigidly fixed.

Also keep in mind that you are using a structure designed for this purpose - the pole previously discussed here are not designed for vertical mounting - they are intended for rigidly being fixed to a building to carry something inside them.

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

Serowe,

Sorry, but I am not being notified of replies to my posts.

The flag pole which is 20' (6.096 m) in height is in a PVC tube sunk in rock approximately 18" (45.72 cm). The pole can be removed for changing the batteries in the sensor station. At 2 and 5 feet up is a clamp which is tied into the fence behind it. The remaining 15' of pole is unsupported. I have a bent pipe at the top to adapt the pole to the sensor station pipe secured with two stainless steel hose clamps.

My post was in regard to other posts talking about resistance of round and square posts and the bending under stress. Last night this pole, with flag up, sustained 35 mile per hour gusts with out any problems. BTW pole is 2.25 inches in diameter and about .094 inches wall thickness, so it is not very heavy duty.

I am not saying that for some installations guy wire should be used, just not necessarily for 2 meter pipe.

BBQSteve

Thanksa for that - and I agree about 2 metre poles not requiring stabilising. 5 metre poles, which has been discussed here, are a completely different kettle of fish though.

Also - the difference between what you have, and others are contemplating - proper ground 'mounting' and diameter of the pipe itself.

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

I think I am going to just go with a thinner pole 2500mm long
http://www.aluminiumwarehouse.co.uk/Alu ... _info.html
attached to my current pole (which is about 3000mm long 40mm dia alu).

I will have it overlap by about 2000mm so it will only extend a further 500mm just to give me
a little bit more height, and avoid being instable.

The current main pole is attached to my shed via two mounting brackets
so hopefully this will be enought not to have swaying.

_________________
Cumulus Real Time Data Grabber
http://bit.ly/WjBh5z

Wokingham Berkshire - weather station
http://www.wokinghamweather.co.uk

MRD Photography
http://www.mrdphotography.co.uk