Author Topic: Freestanding aluminum tower? (Read 7615 times)

elt · « **on:** July 17, 2007, 02:07:21 PM »

I've been looking with envy at the freestanding towers I've see folks make and am wondering if I have what it takes to make one too.

I have three hundred 54" lengths of 1.25" OD .062" wall aluminum tubing. It is seamed.

I don't know what kind of alu it is but it is pretty hard. (I bought it surplus 5+ years ago but then decided that it was too heavy for my application, now I use 1" .050" wall....)

I was wondering if one piece would be be enough for tower legs (am thinking 30' tower for my 10' mill) though I did come up with the idea of tacking three together. Six pieces make a pretty chunky 9' long pole...

... even though I have a lots of this stuff I wouldn't want to waste it (because maybe if its feasible I could make a taller tower?)

Any ideas on this would be greatly appreciated!

Thank you,

- Ed.

Slingshot · « **Reply #1 on:** July 17, 2007, 08:17:22 AM »

Ed,

That's pretty flimsy stuff - are you planning to somehow connect it all together to form some sort of box-section pieces that will stack? Having such short pieces to work with seems like it would be a nightmare to try to make a large structure.

I don't know what you paid for this stuff, but another option would be to sell it and buy a nice Rohn tower. At today's scrap aluminum prices, you have easily $1000 worth of aluminum. That translates to a pretty substantial tower, even if bought new. That way you will be getting something you know is engineered for your application.

DanG · « **Reply #2 on:** July 17, 2007, 08:22:22 AM »

A true tall tower probably is out of the question as aluminum fatigues over time where iron does not - but for a lawn art (<20') tower or solar tracker frames, or even solar heating collector using Al safe coolant looks like you have quite the stash!

Mary B · « **Reply #3 on:** July 17, 2007, 08:32:53 AM »

Aluma Tower Company has been around for many years http://www.alumatower.com/ so aluminum can be used for a tower but the problem I see is properly engineering the tower to minimize flexing.

elt · « **Reply #4 on:** July 17, 2007, 12:29:01 PM »

I guess I don't see these tubes as "flimsy" but maybe I'm wrong...

I'm thinking in terms of strength and stiffness. This page -

http://www.kastenmarine.com/alumVSsteel.htm

- and others give a good argument that, pound for pound, aluminum is as strong as or slightly stronger than steel. The density of alu is a little more than 1/3 of of steel so I was thinking that three tubes together would be stronger than an 1.25" OD, 1/16 wall steel tube. I don't know whether a steel tube that size would be flimsy or not. My tower experience is limited to ham radio towers and isn't that great but I've never seen one with steel as thick as 1/16"

But stiffness in a thin wall tube goes as the square of the OD (and only linearly with the wall thickness.) I'm not sure what the factor would be for welding three tubes together into a larger tube but I'm thinking that it would be much stiffer than a 1.25" .062" wall steel tube... that's something that can be measured so I'm thinking I'll ask my welder guys to weld up a 9 foot pole for me and I'll see.

- Ed.

elt · « **Reply #5 on:** July 17, 2007, 12:40:02 PM »

I've got enough pieces to make a 20' diameter geodesic sphere ... that'd be a pretty cool piece of lawn art!

elt · « **Reply #6 on:** July 17, 2007, 01:18:21 PM »

I was thinking something like this for a 27' tower

http://www.otherpower.com/images/scimages/6527/tower_04.gif

built in 9 foot sections. Piece count is approximate as I don't know anything about tower design and in particular what the side angle should be and how you figure out the space between bracings.

- Ed.

bob golding · « **Reply #7 on:** July 17, 2007, 02:45:28 PM »

hi , i notice those aluminium towers are for wireless and comms use. dont see any referance to wind turbines. think the loading might be an issue. you really need to get a structural engineering survey done on your design before you try to go to any sort of height. i am sure there is software to do this but you might have to go to a specialist to find out. i have used aluminium triangular sections for stage lighting. that stuff is a work of art and costs about the same. we still managed to bend some at a gig. it went very quickly i seem to remember. the rigger came down his rope very quickly too. think by the time you have designed and tested it you wont gain a lot over a manufactered tower as already been pointed out.

cheers

bob golding

Kevin L · « **Reply #8 on:** July 17, 2007, 04:54:40 PM »

Aluminum has nearly no elasticity. It goes directly to to plastic state when placed in torsion or shear. Steel will flex and return to its original state, aluminum will not. When you plan to place a large load on a tower the tower needs to flex and return to its original shape, and aluminum just will not do this. Use aluminum where you need to save weight and steel when you need strength. Sell it and buy a rated tower for your intended use.

Kevin L

thefinis · « **Reply #9 on:** July 17, 2007, 05:58:34 PM »

You have a cool stash of al tubes there and even if you could build a tower out of them it would not be putting them to a good use. Hang on to them a little longer and look for something else stronger and longer to build a tower with. Weight can be a good thing in a tower especially if it is close to the ground. Although a dome with a wind turbine on top would make for a fine conversation piece.

Finis

joesfoundry · « **Reply #10 on:** July 17, 2007, 11:05:51 PM »

at most he would get only 80 cents a pound for that so the tubing is more valuable than selling for scrap. Look on ebay for something to weld aluminum, or heck make you own all you would need is an alternator that can kick out around 150 or 100 amps. Oh aluminum tubing is extruded aluminum, pretty much 1100 series or dang near pure aluminum. I would think with plenty of bracing and in 5 foot sections you could make a lattice type tower. Heck atleast try it....if you ruin all that aluminum then sell it for scrap.

elt · « **Reply #11 on:** July 18, 2007, 06:09:31 AM »

Well, that's a good point. If I sell if as scrap it won't matter if it's in the shape of a fallen tower!

Stonebrain · « **Reply #12 on:** July 18, 2007, 08:44:53 AM »

Yea,

The dome idea is a good take off for reflection.

The strength of a 3D structure composed with triangles depends on the thickness of the tubes but also to the amount of tubes per surface of the shape.So,when the triangles are smaller the structure is stronger.

Even with much tinier tubes you can make a pillar for a bridge,if you put enough of them together.

Take a very steep pyramid and divide every side in triangles adapted to the length of your tubes.You can make it as strong as you want.

All depends if you find an strong and quick method to joint the tubes at the connections.Forget about welding.

Be ingenious,I don't have solutions ready to use idea here.

Don't sell them as scrap for buying a ready made tower.Just because that's no fun.

good luck!

cheers,

stonebrain

Mary B · « **Reply #13 on:** July 18, 2007, 10:12:46 AM »

lots of aluminum tubing is 6061T6. No way to tell what he has unless it is marked.

elt · « **Reply #14 on:** July 19, 2007, 07:22:44 AM »

I'm really encouraged by my tests so far -

I brazed three of the tubes together with 9 one inch spots, three on each end and three in the middle. I suspended the beam across saw horses 4 feet apart and hung almost 300 pounds in the middle of for 10 seconds (about as long as I could hold on.) When I took the beam into the shop, it was still straight ... it's definitely not flimsy!

My original idea was to hang one piece out a few inches so two beams could be welded together without additional parts ...

... but I think that I may get a stronger union if I stagger all three.

This was my first shot at aluminum brazing and I think it was pretty easy considering that I had to do the heating with only MAPP gas in a propane torch... it just took a long time to heat each joint.

I do want to weld the poles but my flux core/MIG welder isn't set up for gas yet. My local welding supply wants about $200 USD to get me a regulator, a 40CF tank and my first fill of argon. OUCH! It looks like regulators go for about $25 shipped on ebay and I'm just going to have to keep my eye out for an good deal on a small used tank before I can move this project forward... (I can trade lots of alu tubing if anyone is interested in a trade!)

- Ed.

bob golding · « **Reply #15 on:** July 20, 2007, 04:44:08 AM »

i am no expert but i think to weld ally properly,IE to get good penetration, you need to use a tig machine and AC. do some test welds and then cut them apart to see how much penetration you get. i am only going on stuff i learned at college so have no experiance of real aluminium welding. other on this board might know more about the practicalities

cheers

bob golding

Kevin L · « **Reply #16 on:** July 20, 2007, 08:32:00 PM »

You should try super glue, I hear it works well in these applications as well.

elt · « **Reply #17 on:** August 14, 2007, 04:12:45 PM »

Kevin L wrote:

You should try super glue, I hear it works well in these applications as well.

Well, I tried it and want to warn any readers of this thread to not follow Kevin's advice. I superglued three pieces together, supported it on each end and went to stand on the beam. It broke apart and I fell on my! But the braised beam was not only strong enough to stand on, I also jumped up and down on it with my considerable overweightage and it held together just fine.

Still, braising was pretty slow so I got set up my flux welder for MIG and got a bottle of argon and went at it... Now this is just my second welding project; the first was the tail for wind mill. It took a lot of fiddling to get all the settings right but I think the welding is going pretty good now. Here's a pic -

There are three roughly two inch long welds on each of the three sides for a total of nine welds per leg section.

I changed the the overlap pattern slightly that I'll be using to join the sections. Previously, I only had one tube staggered, now they all are. The notion is that I'll insert a short piece of (steel) tubing into each end to enable bolting the legs sections together without any bolts interfering with other bolts. Here's a picture of the end of a leg section -

As far as designing a windmill tower, I've googled and studied lots of pictures of windmill towers. I've gotten a notion of generic proportions and bracing from them. One question the pictures left me with, though, was whether to make a three or four sided tower. And what's the difference anyway? Well, I think I found the answer!

This page: SIZING CONCRETE PIERS FOR TOWER LEGS is a real goldmine. (Basically, you'd need twice the shear strength in the legs and twice the diameter in the footings for a three sided tower that you would need in a four sided tower. Even so, I'm leaning towards a three sided tower. I don't pretend to follow the "soil science" but I can do the math and it tells me that I can do the footings for a three sided tower (and have a nice safety factor) with a the 12" auger that I can rent from the hardware store down the street.

- Ed.

dinges · « **Reply #18 on:** August 14, 2007, 04:32:08 PM »

"I've gotten a notion of generic proportions and bracing from them."

Have you gotten this notion for steel towers or for aluminium towers ?

I don't have to tell you that steel has very different material properties from aluminium. Compared to plain steel, aluminium has very low tensile strength (depends on the exact material and the heat treatment), much lower elasticity modulus (E) and of course much lower density. Unlike steel which suffers only from fatigue when the stress cycles have a certain minimum value, aluminium WILL fatigue even when the cyclic stress is small. The fatigue limit/strength of aluminium is zero; given enough cycles, aluminium will fatigue even at 1 N/mm^2 stress.

When welding aluminium, you will change its properties even more. If the aluminium was originally, for example, -T6 quality, by welding it you will in effect undo heat treatment.

I'm no expert on towers or on aluminium. But I would do some -very- thorough research before welding my own aluminium tower.

Plus, I wouldn't even dream of welding a tower without being -very- proficient at welding. From your experiments I deduce that you are new to welding aluminium.

Then again, perhaps Zubbly is right and I worry too much...

dinges · « **Reply #19 on:** August 14, 2007, 04:37:25 PM »

I forgot:

If you don't know what grade aluminium you have, you will NOT be able to select the proper weld filler material !

I assume the shop where you have bought your aluminium wire had a choice of -at the very least- two materials/wires (AlMG and AlSi, perhaps with varying amounts of Mg or Si).

They are NOT interchangeable; well, at least, not for TIG, which is the only aluminium welding process I'm a little familiar with.

ghurd · « **Reply #20 on:** August 14, 2007, 04:47:18 PM »

Most guys don't trust super-glue for holding magnets in AC conversions.

Some guys don't trust epoxy.

Sorry for the misfortune, but beware of unproven suggestions...

My wife removed super-glued neos from an AC conversion a couple hours after they were set.

She simply popped them off like they were never attached.

That is the exact moment I lost ANY faith in super-glue.

Nice welding, BTW.

I am mostly relegated to hose clamps. :-(

G-

dinges · « **Reply #21 on:** August 14, 2007, 06:25:34 PM »

Sorry for the 3rd post in a row, but I realized only later an important detail:

You have switched over your machine from steel wire to aluminium wire. In that case it's important to exchange all feed components of the machine as well (rollers, liner, nozzle). Steel welding wire is coated with lubricant. This lubricant has found its way onto the feeding components and will contaminate your aluminium welds. Therefore you must install new feeding components that you will only use for aluminium.

Just something that I thought of later.

The more I think about it the worse I feel about your project. I know this is not what you wanted hear... I think you lack in 3 important areas: material knowledge (material characteristics of aluminium), tower design knowledge and welding capability.

There's a lot more to welding aluminium than meets the eye.

BTW, you might want to work on your technique; there's an end crater in that weld. With aluminium (TIG), I find that stepping back (1/2 cm) before finishing the welds reduces most of the crater. You might also want to try to keep the bead as constant as possible, if only to prevent stress concentrations.

elt · « **Reply #22 on:** August 14, 2007, 08:10:04 PM »

I confess that I did search ebay for hose clamps before I went to welding! Forty or so would have done it and they were going for about 1/3 price.

The main thing that the welds do is keep the legs from twisting until the cross bracing is put on... I think that the welds will work a little better at that then hose clamps though I honestly believe that hose clamps would be viable in this application... I just think that it would scare the neighbors to see them on the tower! (BTW, I do use hose clamps to hold the tubes together while I weld them. )

- Ed.

elt · « **Reply #23 on:** August 14, 2007, 09:05:21 PM »

Hi Peter,

I really do appreciate your concerns. I'll say a couple of things WRT them:

I think I'm at least as smart as the average tower designer, just not as educated with regard to the subject. But before I made my wind mill, I'd never carved blades, wound a coil or handled NEOs... I think I have two things going for me: First, I have a pretty good track record in 50+ years of learning as I go and, second, I have enough tubing for three towers!
I have done some research into the material properties of aluminum vs steel. In my business, I deal with aluminum truss tube systems on a daily basis. Nothing that has to hold something as heavy as a mill covered with ice in a wind storm but at least stuff that has to hold components to optical tolerances.
Welding: Yes, I have a long way to go! First round on this was folks telling me that I needed a spool gun or a teflon liner, that I'd never get alu wire to feed though my (cheap) gun... honestly, it wasn't that hard. I don't know about contaminations in the liner. I have visited with the guy that does my work-welding twice for advice. So far the only feedback he's given me about stuff in the weld is that "white is okay, black is bad." I did read on the Lincoln or Miller site about backing up at the end to fill the crater but for me at this point there is too fine a line between filling the crater and burning through the tube. What I told my welder guy was that I was only a third of the way done with making these sections (I have 6, need 18) and that I was just going to keep welding; that I'd be better when I got to number 18 and then I'd go back and fix up the earlier ones.

In fact, I do have a free standing steel tower. It's made from rolled and stamped sheet metal and scared witless about putting my mill on it! I really, really believe that what I'm building is a much stronger tower. And if I'm wrong, my alu will be worth just as much as scrap in the shape of a bent tower as it would be in the shape of loose tubes.

At any rate, I'm not trying to refute your advice, only trying to say that I've given some deep thought to many of your concerns. I do really appreciate your posts. I might be wrong in my thinking about things but at least you've got me thinking that I've been thinking about the right things.

Thank you very much,

- Ed.

Kevin L · « **Reply #24 on:** August 28, 2007, 11:53:42 AM »

Elt Wrote:

I superglued three pieces together, supported it on each end and went to stand on the beam. It broke apart and I fell on my!

Super glue and aluminum poles, I cant think of a better application for a wind tower installation.

If you did really jump on this you should think about application of some basic safety practices in your shop. Some weights a 1/2" of the ground tied to some rope would have worked just as well. I wish you the best of luck with your tower, but advise you to keep it clear of areas where people or property exist, or someone may end up with something worse then a scratched bum. Oh and to apply a accurate test to your weld, you should weld the two 54" ends together and then support the 108" length ends with the weld being in the center. Apply the weight to the center joint and test for weld yield strength with weights. When your done, if the weld doesn't break, let us know how straight the length is after the test, as it will not flex back to its original as steel would have. I really do wish you the best of luck.

elt · « **Reply #25 on:** August 28, 2007, 12:37:55 PM »

When your done, if the weld doesn't break, let us know how straight the length is after the test, as it will not flex back to its original as steel would have.

I can always add enough weight to permanently bend the aluminum poles. In fact, I can always add enough weight to permanently bend steel poles too. Unless you can tell me how much lateral force a freestanding tower leg should withstand, there's not much point in doing any test... what would the result mean?

Even through I'm using different materials, I'm engineering my tower to be the structural equivalent of this tower ...

http://www.universaltowers.com/pdf/HD_models/01-model%23-hd-35-40.pdf

Did you think I was just winging it? And "no" I wasn't stupid enough to take your suggestion literally. I recognized your sarcasm; I guess you didn't recognize mine.

- Ed.

pepa · « **Reply #26 on:** August 28, 2007, 01:17:16 PM »

hi Ed, i was following your post and then forgot about it until i saw Kelvin L's response. the three pole design should work if you can work out the splice joints and have good truss bracing for each section. my thoughts on the splices would be to forget the extensive welding and use collars insted.

take some of the pipe and cut it into lengths that when hammered flat, would rap around all three poles with a flange on each end to allow for bolts to pull the pipe togather tight. use these in the center of each section and make one more for each offset pipe joint (three for each leg joint) and long enough to mold to the shape of the three pipe unit. but mount tne sections and draw tight with the two bolts on the flange then add a bolt through the flange and two of the pipe. the center bolt will use one bolted pipe and one the unbolted pipe. the bolts could also be used to hold the ends of the truss bracing if the three pole leg is turned right. hammer flat the ends of the braces for the bolts and washers.

i made roof trusses for a living at one time and demonstrated the strength of the 2x4 trusses i made by driving a pickup truck onto and up a plywood roof section that i had build on the ground for this purpose. hope this helps, pepa.

Kevin L · « **Reply #27 on:** August 29, 2007, 09:16:20 AM »

I can always add enough weight to permanently bend the aluminum poles. In fact, I can always add enough weight to permanently bend steel poles too. Unless you can tell me how much lateral force a freestanding tower leg should withstand, there's not much point in doing any test... what would the result mean?

True enough, we don't know the exact loading as we don't know the size of windmill or design of your tower, and given enough aluminum you can probably make this strong enough to support a windmill. But given the fact that we don't no the loading there is room for error, and given the prices of aluminum and time I still think you would be better positioned to install a known system.

If you are basing your system from the Universal Tower designs you should keep in mind (having a HAM background) that these towers are designed for antenna's. These antenna's have small surface area's. The specific tower you listed would limit your windmill to a maximum radius of 3.31 ft. I would make it less given your tower system would be home constructed, without the testing facilities or in depth engineering calculations. Even the Model 35 -30 which is 30 ft tall is still limited to 34.5 sq ft @ 80 mph. Hardly a electrical powerhouse at 27 - 40 feet given the amount of money and time you will have invested in the tower. Even if the aluminum doesn't represent real money to you, there is value to the aluminum and it should be considered.

Sorry I didn't recognize the sarcasm in your direct statement. Apparently others didn't recognize either of our points of sarcasm.

I think its great that you found that fantastic deal with the aluminum. I would look for other uses is my only point.

I wish you the best of luck.

elt · « **Reply #28 on:** August 29, 2007, 03:56:01 PM »

I would make it less given your tower system would be home constructed, without the testing facilities or in depth engineering calculations.

Seems like you're making an assumption that I am incapable of testing or in depth engineering calculations.

- Ed.

Kevin L · « **Reply #29 on:** August 29, 2007, 11:09:45 PM »

Given that you are jumping up and down on your test welds, I would say this is a correct assumption. Unless you are paying to have the types of testing that are done here then your calculations are all based on assumptions. Last I heard you didn't even know the grade and type of aluminum you are working with, thus my statements are not assumptions, but based on the reality of the information you have provided. You are getting welding advice from your local weld shop, and while I'm sure he is a very skilled welder, this is no way substitutes for a Metallurgical Engineering Staff that is employed by Universal Tower Company. I am certain that they do conduct this type of testing as they would be unable to certify their products for commercial sale unless it was completed. I'm not trying to be rude, but tower load calculations are not as simple of an endeavor as you seem to think it is. They require a slew of destructive tests just to determine basic weld strength and penetration depth. It is your money and time....

Kevin L · « **Reply #30 on:** August 29, 2007, 11:34:35 PM »

And you were really considering the use of hose clamps??

elt · « **Reply #31 on:** August 30, 2007, 06:35:10 AM »

Well, I guess I have enough experience at destructive testing and determining system failure modes that I can get a good feel for what's going on by jumping up and down on a part...

I don't know if you're one of the people that like to engage in endless and pointless debate with people or what; I am not.

Goodbye,

- Ed.

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Author Topic: Freestanding aluminum tower? (Read 7615 times)