Tower question

[willib]

What if a tower was mostly cables and rods?

would that work , or is it Too complicated?

The horizontal bits are rods, the cables are connected to the rods and the center pole as are the rods.

I may be daft but it seems to me that if i was gonna make a tower out of a pole that is too small in diameter to support the weight on its own , i was thinkin why not beef it up a bit?

[angus]

Willib - No you are not "daft", and yes most towers are made of cables and rods- one rod up the centre and guy cables around.

No your design will not work.

Why? Well look at your ground connection- ie. at the slab .Your drawing shows how you are trying to transfer all the stesses out or the centre pole only to transfer them all back again at ground level.This is where your tower will fail.

So you try to "fix this " by spreading the cables at ground level -only to find that your tower will fail at the next "connecting node" ie. at the top of your first diamond shaped cable/rod stucture- there are 3 of these in your drawing. So you try to fix this as well by again spreading the cables to ground- and so on .

So before you know it you suddenly have a traditional "pole-guyed to ground " tower.

What you are failing to understand is that a centre pole is quite capable of supporting the weight of a mill - just take a piece of 3 inch pipe about 4 foot long and sit the mill on top of it- it will stay there forever.

HOWEVER if you now sit the mill atop a 3 inch pipe that is 100 foot long it will buckle. This is where guy wires come in- to stop this buckling- and your design will not prevent this buckling.

The above only adresses the mill static load. When you need to factor in all the dynamic loads. matters become even more complex and critical and a wind turbine tower has got to be one of the most dynamically stressed structures I know of.

Sorry no offence intended.

Regards

Angus (The older I get, the better I was).

[SparWeb]

You could argue "on paper" that it can be done safely.  This kind of bracing is used in some sailboats, I believe.  If you take it too far, you end up with a confusing situation where it becomes susceptible to compression buckling, yet if you tighten the cables thinking that will stiffen it more, you just make the situation worse!  Even under light loads and applied forces, if one of those wires breaks or comes loose, the whole thing comes screaming earthward, so maintenance and testing the rigging becomes a hassle.

The only argument that I can think of to justify such a design is for the weight.  If your tower simply cannot be heavier than "X", but it must be "Y" tall, there could be an extreme case where even the spindliest of truss couldn't make the X/Y ratio.  Then you might resort to something like that.

[SparWeb]

I think he just omitted the guy wires, and isn't expecting this will do away with them.  Assume there are guy wires, and there is a precedent for building things like this.

... not for wind turbines, though...

[angus]

Steve. If he has " omitted the guy wires" and intends to include them  as an addition to the drawing then what is the point?. You may as well use a centre pole of sufficient size and guy wire it appropriately - it would save a heck of a lot of fabrication costs.

I think you have agreed with me -in that if something goes wrong " the whole thing comes screaming earthwards".

There is no argument to justify "if you need to be X in weight but Y tall" then etc.

If the "spindliest of trusses " cannot do the job then this cable/rod structure most certainly will not.

What needs to be remembered is- a wind tower is different.

It does not need to support a load against gravity- like a suspension bridge.

It does not need to support a cantilevered load - like an upstairs balcony extending from the side of a building.

It does not need to cope with changing loads (wind loads) whether they be north,south, east or west or updrafts and downdrafts or even wind shear.

A wind tower needs to cope with all of the above -all at the same time- no easy task.

Flux once said (in response to an earlier post of mine ) "why try to re-invent the wheel". I think his comment is appropriate here.

Again no offence intended so "scuzze"

Regards

Angus (The older I get, the better I was).

[angus]

PS. We all forget (and I am guilty of this- hence the PS) about the gyroscopic forces up at the top of the tower.

Every time the mill yaws to faces a changing wind direction or to furl out of the wind it creates a twisting force on the tower- in order for the mill to twist in one direction it must try to twist the tower in the opposite direction and in doing so there is a gyroscopic torque induced at 90 degees to the mill motion.

This cable/rod structure cannot cope with these twisting forces.

Regards again

Angus (The older I get ,the better I was).

[fabricator]

In your drawing yo don't have nearly enough of the horizontal bits, a tower has to be supported 360 degrees, you would have to have your horizontal spreaders every 20 degrees around the center pole at every spreader, this would get very complex very fast.

[wdyasq]

I think it will work well with a VAWT.... well, at least the builder will able to claim 'The tower failed' ... not that the VAWT wasn't working.

Ron

[Beaufort]

I grew up on sailboats and have played with lots of rigging, and often thought of the application to wind turbines.  The loading on a sail puts much of the force toward the bottom of the mast compared to wind turbine loading toward the top.  I've been amazed at the amount of force that a mast can take in storm conditions and pitching in the waves.  The big difference is that a mast will not buckle when being raised; they're sized to take the spanwise loading and compression loading (to your point).  Checking the tension in the rigging was a very important job for some of the larger boats, and we'd often do this before and after shakedown trials in the Spring to ensure the loading was evenly distributed on all the stays.  We had one let go and the fear of nature is comparable with having an unloaded turbine in a storm.

Some Canadian company offers towers with a spreader lattice like this, but I can't remember if they had additional guys or not.  It seemed like the spreaders were mostly to keep the tower from folding during raising.  I'll have to see if I can find it because it's the same concept as presented here.

[cardamon]

It could work if designed right.  Think about it, a freestanding tower is just a big truss which  works by providing more mechanical advantage against bending on any given member.  Your idea is really just the same thing except you are using some members that only function in tension. I agree with others that at least you would need another set of braces at 90 degrees to the ones shown (Im sure you knew that, after all it is a 2d drawing) and it needs another set going to the ground. It reminds me a lot of Bucky fuller's tensegrities http://en.wikipedia.org/wiki/Tensegrity

[greend88]

I think He maybe wanting to do somethings like the tower on this page: http://www.prairieturbines.com/index.htm

[tanner0441]

Hi

If he wants free standing why not go for a latice tower with a spread base.

Brian

[ChrisOlson]

So you try to "fix this " by spreading the cables at ground level -only to find that your tower will fail at the next "connecting node" ie. at the top of your first diamond shaped cable/rod stucture

As a mechanical engineer by trade, I feel I should chime in here - actually this structure won't fail if the trusses and standoffs are designed correctly.  All it needs is a suitably wide base that extends part way up the tower, or have guy wires at the top.

Triangulated trussed structures like this have been used for years and they are VERY strong.  For instance, I've seen very large screw conveyors (augers) trussed like this with 150' long 11 gauge (less than 1/8" thick), 12" diameter tubes running at a 40° angle, with 10,000+ lbs of material plus another 3,000 lbs worth of steel rotating inside that tube shaking the living daylights out of it - and they don't collapse.  They are trussed identical to the drawing using a heck of a lot lighter tubing than most people use in wind turbine towers.

--

Chris

[ChrisOlson]

you would have to have your horizontal spreaders every 20 degrees around the center pole at every spreader

The truss standoffs only need to be every 90°.  Draw it out on paper using force vectors and this will become apparent.

--

Chris

[ChrisOlson]

I took the liberty of quickly redrawing your design.  This is how I would do it:

A wire rope trussed monopole like this could be easily made to withstand minimum 50 lb/sq ft loading as a free standing structure with a suitable base.

--

Chris

[GeeMac]

A triangle is the most stable of all geometric shapes. Add a few more cross braces and give it a try.

[Perry1]

I don't agree with this one Angus. The gyroscopic forces are absorbed by the blade/hub system and do not transmit through to the tower, at least with a free yaw system like we all use.

There is no way to transmit angular forces to the tower through a freely spinning yaw bearing.

Perry

[Watt]

The top 1/3rd not counting of course the top triangles will flex like crazy on this one.  No tension or load for side to side movement from tip top to to bottom.

[MagZ]

Here is a similar tower design and it is 140ft tall..... and has a good load on it..!

http://www.builditsolar.com/Projects/Wind/TomTurbine/Main.htm

I think it can be done when properly designed, but I think you have to be more carefull with the maintenance of such a design as the aging process is taking it's toll. Usually what goes up will eventually come down, hopefully with a winch.

Cheers, Manne :-)

[willib]

Thanks for all responses , i learned a good bit

on a side note:

I built this about five years ago.

look similar ?

This is the windtronics wt6500 wind turbine lol

http://s7ondemand1.scene7.com/s7ondemand/zoom/flasht_zoom.jsp?company=AceHardware&windowtitle=ac
ehardware.com&zoomwidth=523&zoomheight=565&config=ACEzoom&cs=false&sku=p6696073

of course i posted pics of it on the net.

call me stupid.

Hey i wish them luck with it.

http://www.wind-works.org/SmallTurbines/Windtronics760EstimatedGeneration.html

[don1]

 It appears to me that you were only interested in strengthening up a lighter tube with this idea but I can't help but see a taller tower made this way. I don't think I would be in a hurry to discredit this design at all. First off it is made up of all triangles. They can not fail until you exceed the yield of the material that they are made of. That said I think if I where to build a larger tower I would drop the cable and use all pipe. It was said by someone else already that cable could be hard to deal with. Also when the wind blows on one side of the tower the cable will be in tension and on the other side the cable would just slack. If you used pipe when one side is in tension the other side would be in compression making the structure less likely to yield.

 If this tower was only 30 or 40 feet you would only need one heavy set of guy cables attached to the top horizontal spreader aria. It would be hard to in vision the tower doin the hula dance between the guys and the ground.  

 I think this would be a rather pleasing looking tower to have in the yard and if materials where spected out properly it could be a sturdy unit.

 Good thinkin there Willib

[janschipper]

towers require enough space for the guy cables and a provision for ... At a minimum, all towers should be grounded via copper cables and/or grounding rods/grids and ... This applies mostly if your tower is tall and/or antennas