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Hi ALL,
I'm building a 13m gin pole tower(2 x 6.5m x 2"x 3.6mm)for my 2m chinnese wind turbine and would like to know what size wire rope at the top / middle would be. Thanks Ivan
P.S. I may put my 3m F&P up too.BUGS
Bolty Regular Member Joined: 03/04/2008 Location: AustraliaPosts: 81
Posted: 12:00am 20 May 2009
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I may be being overly cautious but I would be a bit concerned about the ability of a 6.5m length of 50 mm pipe to resist buckling under heavy winds, especially if a 3m diameter turbine is mounted atop. I am not referring to the ability of the pole to take the downward weight, but the horizontal component of the twisting force of the wind load on the turbine.
I would be looking for an internet engineering programme to calculate the ability of the pole to take it!
As a guide, my pole is 115 mm diameter. It was originally the supplied pole with a 6m high 1 kilowatt (2.8 metre diameter)chinese system. It came with 10mm guy wires (definite overkill). I have since extended the pole with more 115 mm pipe to a height of 11m. I am still using the provided guy wires, mounted at a point 8.5 m above the ground. This pole has withstood a storm of 27 m/s when I had 5 m diam blades fitted. The blades exploded, but the pole and guy wires survived undamaged
KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691
Posted: 12:21am 20 May 2009
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Bugs, I have a feeling that you should have more than two sets of guys for a pole that tall, at least four sets.
Thanks Bolty,John
I'm thinking along these lines,4mm s/steel or 6mm gal wire rope?
What do you lift your towers with, e.g hand winch,power winch,4wd or tractor?
13m Tower
height: 13m
base dimensions: 9.2m x 9.2m
outside foundations: 0.6 x 0.6 x 0.6m
centre foundation: 1 x 1 x 0.25m deep
Ivan
All,
I found these cal's on the net,mite be of some youse.
Tower: Overview and Winch
The tower is constructed from schedule 40 steel 2.875" OD tube. It is 36' tall. It is made from a 15' piece coupled with an extruded aluminum coupler. Guy wires support it at the 15' and 30' level. A rotary thrust bearing sits at the top for the generator. Steel plates make up the base which also holds a 15' tube for the lever arm. This is called the Gin pole. 1/4" steel cable serves as the guy wires. The Gin Pole is actuated through a coupler to a chain connected to the winch cable. The pictures below show the tower ready for lifting. The next set of pictures shows the winch setup.
The winch can move 2500lbs. I welded a platform out of 3/16" steel angle iron to give the winch arm plenty of clearance from the ground. The platform is bolted to a concrete pad using 4 1/2" anchor bolts. The concrete pad is 10-12" in diameter and 3' deep. I used 6 pieces of rebar, 4000psi fiber reenforced concrete to reducing cracking, and 18" long 1/2" J-anchor bolts.
Now for some physics. The concrete can withstand 4000psi in compression. Conservatively, it can take 5% of this for shear forces. 0.05 x 4000 = 200psi. Now the surface area of the anchor bolts is pi*D*L, which is
3.14*0.5*(17" of submerged bolt) = 26.7
Now, multiply by the number of bolts = 4*26.7 = 107sq inches
The shear force the four bolts can hold in the concrete is 107 sq in * 200lbs/sq in = 21,400 lbs.
This seems like a lot. The bolts will give before the concrete lets them go. In other words, the winch is not moving anywhere.
What forces will the winch see? The tube weighs under 6lbs/ft and is 36' long. The generator, blades and tail probably weigh close to 60lbs.
Tube: 6lbs/ft * 36ft = 216lbs. Center of gravity at 18'. Momement = 216*18 = 3888ft-lbs
Generator moment: 60lbs * 36ft = 2160 ft-lbs
Total moment = 6048 ft-lbs
The maximum force will be when the tower is at zero degrees and the gin pole is at 90 degrees. The 15' gin pole needs a moment equal to the tower-generator moment:
15' * X = 6048
X = 403lbs
The winch cable pivots 20' from the tower pivot and connects to the top of the 15' pole, making an angle of 37 degrees. Using basic trig:
403/F = cos(37)
F = 504 lbs
So, my winch will easily handle 504lbs of tension on the cable.
BUGS
Bolty Regular Member Joined: 03/04/2008 Location: AustraliaPosts: 81
Posted: 12:10pm 20 May 2009
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I cannot really comment any further due to the fact that my pole is erected by an adjoining support pole that has a pulley on top. It is therefore substantially different to a gin pole set-up. My original concern remains that the 50 mm pole requires stiffness to prevent buckling. Of course an extra guy point would provide this. As for the size of the guy cables, I would recommend a calculation of the foreseeable forces on the cables. I think from memory that 6mm cable has a breaking strain of around 1100 kg (depends on the kind of cable). From what you have described, I would suspect that your cable strain would be a lot less than this and that 6mm should be adequate. However I would not be happy to rely on this feeling without checking it out quantitatively!
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 12:34pm 20 May 2009
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Ivan, gal wire is more suitable for this application, its cheaper too. If you don't have a swaging tool for the end eyes and are planning to use those squeeze grip clamps, make sure you get a wire cable with a *wire* core, not rope as this squashes the cable flat under the clamps.
Re raising the tower, in the long run it would pay to have a support frame to about halfway up where the mast see saws off, for very easy raising and lowering. There will be times you want to lower it in a hurry.
Klaus
SparWeb Senior Member Joined: 17/04/2008 Location: CanadaPosts: 196
Posted: 06:53pm 20 May 2009
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Ivan,
Where are the safety factors in your analysis?
Aim for SF>4 at all points because gin-pole-raised towers bounce and wiggle around a lot. It's not the standing upright - it's the going up and going down that you should be most concerned about.
I've been using my tractor to lower my tower for over a year. Last month the cable came free and the whole thing dropped. It's a hard thing to live down, dropping your own windmill. You've got a winch, so use it. Don't assume that a winch can pull with the same force it is "structurally" rated for.
Steven T. Fahey
Have to sit down and do some cal's and trig to work out the lifting loads on tower.I've been offered 65 x 180 m of fruit netting, which has 10mm cable holding it up.May come in handy for the tower.
Regards Ivan
BUGS
windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331
Posted: 12:30am 22 May 2009
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Ivan how strong are your winds because your proposed two layers of guy wire will not suffice, just not enough. Distance of anchor point from tower base affects this also, a wider spacing creates a less acute angle. The more acute the angle, the top guy is the worst, the more the tower can bend around the cable anchor point.
When raising and lowering there is a point, about 20 deg. off vertical when the lower part of the tower wants to bend towards the raising point, the weight on top overcomes the towers ability to resist bending. You are then left there seeing your tower bent double, turbine on the deck scratching your backside saying what the!!!! It is necessary to hold the center in the opposite direction to keep the tower straight, Bergy describe this on their site.
allan"I like this place and willingly could waste my time in it" - (Act II, Scene IV).
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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