Planning a new tower

[SparWeb]

This has been a long-term thing that I've picked at for years.  This year I may be ready to finally take the plunge.
I'm looking for suitable towers about 60 feet tall that can take a decent wind load.
I also want it to be a self-supporting tower so that I can get away from guy wires all over the place.

A few years ago I built a radio tower for my internet and TV antennas using a truss-tower, and I'm very pleased with how that one turned out.
I also discovered the benefits of using screw-pile anchors so I'm going with that, too.

I haven't done a stress analysis yet so I don't know where the weak spots are yet.
I'm just getting started by eye-balling the sizes of parts.  Mostly it's 6x3 inch HSS rectangular tubing with 5 inch OD tubing for the hinges.
Here are some screen-capture images from On-Shape where I've been drawing it up:







[ Specified attachment is not available ]

[Adriaan Kragten]

To me it doesn't seem logic to use a foundation with four anchors for a tower with three legs. I have built a 12 m slender free standing tower with three legs made of pipe and I used a foundation with three vertical strips poured in a trangular block of concrete. Each tower leg had a fork at the bottom which falls around the foundation strip and tower and foundation are connected to each other by three heavy bolts. Two of the three bolts were used as hinges to topple the tower. These two bolts were also used for the auxiliary tower which was used to lift the tower by a winch and two strong steel cables. The 5 m long auxilary tower was made from two pipes welded together at the top and flattended at the bottom.

A disadvantage of using 60° angle iron is that the tower will get only a very low torsion stiffness. This may cause torsion vibrations due to slip stick of the head bearing. Using pipe for the legs makes the tower much more torsion stiff. The advantage of using angle iron is that the tower can be bolted and that angle iron may be cheaper than pipe per kg. But 60° angle iron is not very standard and it may be much more expensive per kg than 90° angle iron

I have also made a 6 m slender 4-legs free standing tower made of 90° angle iron and strip welded together. The advantage of 90° angle iron is that the holes for the bolts with which the tower legs are connected to the foundation, can be drilled directly in one side of the angle iron. However, the area around the holes has to be thickened to prevent a too high thrust pressure.

[Mary B]

Rohn uses this on 25g towers to 100 feet... I have one on a 30 footer. Just to give you ideas...

[SparWeb]

Adriaan,
Funny, I didn't think of making the whole tower myself.  Here is the type of tower that I plan to buy:
http://www.trylon.com/products/stocked_towers.aspx
There are many choices (also see the link below).  I have bought used towers in good condition and I am looking for another tower that I can buy used so that I can afford a sturdy one.

I am using 4 anchors so that a square base can be made to stabilize not only the tower hinge but the gin-pole hinge at the same time.
The gin-pole, being a column in compression, leads to end-fixture loads and moments that you may be able to appreciate are very high, and permit early collapse of the gin pole if they are not controlled with sturdy hinges.  The compressive loads are quite high when the tower is being tilted therefore both components of the base need to stabilize the system.

Mary,
I'm not against the tubular legs, but they do make the tower heavier = more difficult to tilt-raise.
I have looked at the Rohn towers, too.  A Rohn 25G is much too small for a wind turbine.  Perfect for my weather station, though.

By the numbers, this RSL is strong enough: http://www.texastowers.com/rsl60l50.htm
But I don't disagree the tubular legs of the Rohn SSV are much much stronger. 
They're also probably too heavy for me to deal with as easily.

I offered a few dimensions in the blurb, but I didn't make it clear - this will be a fairly big tower and I'm aiming for 60 feet, too.
This is one idea I have for an adapter that allows the tower to hinge up with a gin-pole but easy to tighten and secure once it is up. 
The clamping on the hinge tube restricts the "wiggle" that you would get on crappy bolts like the ones on the hinge of that Rohn tower in Mary's attached photo. 

Here's a picture of the similar base that I built for my radio tower a few years ago:

[Adriaan Kragten]

So what I call an auxiliary tower you call a gin-pole. I didn't know that name. It's true that you get a high compression load in the gin pole so the gin pole has to be checked for buckling. The compression load can be calculated rather easily if you know the weight distribution of the main tower and the head and the pattern of the cable from the tower to the top of the gine pole and the cable from the top of the gin pole to the winch.

For buckling calculations it is assumed that the force acts in the centre of the pole. In the formulas for buckling, there is the factor lambda which is L / i. L is the length in between the ends of the beam and i is the radius of inertia. If L / i is larger than 200, which will be the case for long gin poles, you have to use the formula of Euler to find the maximum allowable compression load. The radius of inertia i is the square root of the ratio I / A. I is the lowest moment of inertia and A is the cross sectional area A of the chosen beam. i is high for a pipe and rather low for 90° angle iron of the same cross sectional area. So for the gin pole, you should always use pipe.

The formula of Euler can be found in handbooks of mechanical engineering. You should use metric values in all formulas.

[Mary B]

With the higher load forces get your mounting plate flat to the concrete if possible! Otherwise you are suspending leg stresses out in the air in between mounting points...

That was why I showed the rohn base. Just as an idea to mount the tower flush to the concrete to better handle stress loading... another example for my TMM433hd. After the 2x4 support forms were removed high strength grout was packed under the base. And the base mounting bolts into the concrete are directly under the leg attachment points.



That base is for an angle steel leg crankup 33 foot tower that is super heavy duty to handle my severe weather(50 square feet of wind load)

[SparWeb]

Some of you may remember my concrete base disaster a few years ago:



Never again!

The screw piles are stronger, cheaper, and easier.

[SparWeb]

Mary,
Where do you attach the gin pole on that setup?
Those stubs don't look as strong as the tower legs.  Relying on a single weld in tension?

The TMM433HD allows 30 square feet area at 33 feet tall.  Though my goal is 60 feet tall, my area is about the same, so I'll look closer at the TMM's.  There might be a taller option that suits.  Thank you

[SparWeb]

Another way to hinge the legs:

[SparWeb]

Here's an example of that hinge, used on a Rohn SSV.  Huge tower - bigger than I need.
Notice how the leg plates of the tower don't line up with the plates they put hinges on.  Rotated 30 degrees.  Looks like a rookie mistake, though they may not have had a choice.

[Mary B]

Mary,
Where do you attach the gin pole on that setup?
Those stubs don't look as strong as the tower legs.  Relying on a single weld in tension?

The TMM433HD allows 30 square feet area at 33 feet tall.  Though my goal is 60 feet tall, my area is about the same, so I'll look closer at the TMM's.  There might be a taller option that suits.  Thank you

I didn't use the optional gin pole. Since the tower cranks down to 12' we walked it up with 4 people then attached the antennas. But that base has the attachment points for the gin pole/winch setup if I want to add it(spendy! I would build my own)

[mbouwer]

It seems very valuable to me to put together a calculation for a free standing 60 feet tower, without guy wires, with your mill type on top.

[SparWeb]

I didn't use the optional gin pole. Since the tower cranks down to 12' we walked it up with 4 people then attached the antennas. But that base has the attachment points for the gin pole/winch setup if I want to add it(spendy! I would build my own)

Oh, I see. Collapsed down it isn't very tall.  I just realized that this one is like the towers that are mounted on trailers for mobile radio repeaters.  Of course, it's obvious now.
Would a crank-up tower really be suitable for a turbine?  I'd be putting ~200 pounds on it.  I kind of doubt that.

For me, analysis is part of the fun.  I know, not everyone enjoys doing the math.  I like the insight it gives into the efficiency of the structure.  Adjusting parameters and seeing the effect on the safety margins helps build intuition about what is safe and unsafe, and optimizing structure with the least cost penalty.  These projects are also opportunities to explore new methods (to me) and new software such as FEA (Finite Element Analysis).

Since some of you say you are interested in analysis, then I would be pleased to share what I find in that regard.  I currently have some pieces in place that will allow me to confidently buy a specific tower that will meet my needs.  That does not yet have the details about the mounting and tilt-lifting, though.  I will not begin the final analysis until I have chosen a specific tower, defined the weight and dynamic loads of the turbine I'm planning (16 feet), and chosen the mounting and lift mechanism.  I am closing in on approximate values for all of these parts, but none are solidly confirmed yet.

Still considering various ideas, and greatly appreciating the suggestions that I'm getting so far!

[Mary B]

Mine would easily support a smaller 6' turbine, but they doubled in price not to long ago and it is WAY to expensive these days. An SSV type tower is far cheaper and you can build taller.

11'x11' H frame, four 20 foot long antennas, 75 pound rotor... I probably have close to 200 pounds dead weight and a LOT of twisting force up there.

[Mary B]

For those using guyed towers this is an option to not need to climb!

http://www.antennapartsoutlet.com/Pages/Products/HazerPages/H4.html

You would need to build your own and make it heavier duty...

[bigrockcandymountain]

16 feet.  Does that mean the toshiba is going up? I would be excited to see that happen.

[SparWeb]

Shhhhh....
You'll spoil the surprise!

[topspeed]

It seems very valuable to me to put together a calculation for a free standing 60 feet tower, without guy wires, with your mill type on top.

That is a mighty tower. Can you approximate the cost of that ?

[SparWeb]

I will do an estimate once I've chosen a design.  It depends on how much of the tower is bought rather than built by me, of course.

[Mary B]

There is a ham in WI selling surplus broadcast tower sections, 20 footers that are broken down for shipping... if interested I can get you the guys name in a PM...