FreestandingWinchargerTowerAnchorInfoNeeded...

[doubledipsoon]

I'm about ready to drill the foundation holes for my sixty year old 45 foot three-legged self-supporting Wincharger Tower. The tower has a 92" spread at the base. I'm not an engineer, but from the info I've gathered over the years, I've decided to auger out three 7 foot holes, each three (3) feet in diameter. That would amount to about 1.8 cubic yards per hole of cement, for a grand total of 5.4 cubic yards for the three holes. My soil is clay/ rocky, with no sand. Now, I'm mounting a Sencenbaugh 1000-14 wind generator on the Wincharger Tower. This bird has three 6 foot blades, with a top RPM of 290 before it feathers out of the wind with its "blade-actuated" governor. With all the above info, do you think there's enough cement in those holes to secure this baby? Do I get an "A"?

[Crispy]

I think I read on here somewhere recently that a cubic foot of concrete weighs around 150 Lbs. If that is accurate then you are looking at almost 22,000 Lbs. That's in the neighborhood of what Chris Olsen used for his tower which I believe is 90 ft. Check with him though. I'm just going off memory.

Don't forget plenty of rebar 

[birdhouse]

off the top of my head, that sounds just a hair light for 92" spread.  but i'm no engineer.  45' is a large pivot arm!

5.4 yrds ~ 21,600 lbs...

one things that's easy to do if your nervous, is to climb down into the holes and dig out the sides a bit.  give a hair more room for concrete, and pull out is less of an issue, not to mention a larger bearing surface on the soil below. 

adam

[doubledipsoon]

Chrispy, Birdhouse, thanks for the replies- Yes, I'll be using alot of rebar, and upward-facing metal "hooks" on the anchor legs. As far as the suggested conical/fluted shape of the holes, yes, I have considered it, and probably will get my breaker bar and do a workout on the holes. It was recommended by Michael Hackleman in his famous book, "The Homebuilt, Wind-Generated Handbook". I'm fairly OK with my plan, but I am paranoid about the "catch 22's" involved in the lateral thrust produced by this wind generator. as it has beefy blades like a "Jake". That's why I'm using "overkill". Thanks again for the input.

[Mary B]

my 64 foot ham tower that was free standing had a 5x5x5 foot block of concrete under it with lots of rebar. Not as much wind loading but a starting point. Here are the calculations if you like heavy math http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&ved=0CD4QFjAB&url=http%3A%2F%2Fir.uiowa.edu%2Fcgi%2Fviewcontent.cgi%3Farticle%3D2427%26context%3Detd&ei=rOHpUOHzIomNrAGt24Fg&usg=AFQjCNHwqM0Q41pHQ6btdQG4t0qyyfUvLw&sig2=wXajbfwH_qgJ6FUVTmVDJA&bvm=bv.1355534169,d.aWM

[Crispy]

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Re: solar hooked strait to the battery question
« Reply #10 on: January 03, 2013, 03:19:11 PM »

    Quote

Yeah, guyed towers aren't really any cheaper than self-supporting.  You need 25 tons of concrete in the foundation of a 80 foot self-supporting tower in most soils.  But that's a nice trade-off for the amount of real estate guyed towers take up, plus having guy wires strung all over tarnation.

The above was Chris Olsen's reply the other day to a tower question, so I was off by saying you were close to his footing weight.

I'm no engineer either and wonder if adding the total of 3 separate footings is a safe way of calculating because technically each leg will only have approx 7300 pounds. Not sure if Chris's foundation is a single pour or 3 like you propose. It could make a big difference. Sometimes in engineering the total required does not equal the sum of the individual components.

Your tower is 35 feet less than his which should lower your requirement. Question is how much? There are people on this forum that know how to calculate the wind load on a tower but I ain't one of them so all I can suggest is proceed with caution.

[ChrisOlson]

With all the above info, do you think there's enough cement in those holes to secure this baby? Do I get an "A"?

A three pier self-supporting tower is a little different than a one piece foundation because all the loading at the top of the tower structure can be applied to only one pier if the wind direction is right.  On a 45 foot tower with 500 lbs of horizontal thrust at the top, the lift force on one pier is going to be roughly 3,500 lbs with a 92" base on the tower.  1.8 yards of concrete is about 7,000 lbs so you have a 2x safety factor at 500 lbs thrust.

But you really need to know the operating dynamics of your wind turbine to determine that.

The other issue with individual piers is to make sure you're below the average frost depth.  If you're not your tower will lean in random directions due to frost heaving.

I really prefer a one piece foundation for self-supporting towers, but they are more expensive (by usually triple).  The advantage with a one piece rebar reinforced foundation is that loading imposed by one leg of the tower structure is transferred to the whole foundation instead of just one pier, no matter which direction the loading is imposed.

Off the top of my head, if your turbine is the size I think it is (4 meter?), I think you will be OK at 45 feet.  Just make sure you bell the holes by 150%, i.e. if the top of the hole is 3 feet, the bottom of the hole is 4.5' - OR pour an inverted T-type foundation with a 1 foot thick base that is 4.5' in diameter and the rest of the pier is 3' in diameter.  Doing an inverted T-type foundation will require excavating a 4.5' diameter hole, forming the 3' diameter pier, and backfilling when done.

Be careful with pouring that size foundations in cold weather.  The concrete will get very hot during curing and it will crack if you expose it to a wide temperature variation (50 degrees at 7 feet down and below freezing temps at the surface) with a high core temperature in the pour itself.  Pouring 3' diameter foundations is not like pouring a 6" slab.  So unless you are an experienced concrete man I would suggest hiring a concrete contractor to do it  - because you only have once chance to get it right.
--
Chris

[doubledipsoon]

      Chris, MaryAlana, thanks for the replies- Chris, a special thanks for the comment on "horizontal force" of the spinning blades. I would appeciate how you came to that specific "500 Lbs." number? Can you quantify that with your equation? I know there are formulas for "lateral thrust", but I am not aware of them. Just for your own info, this Sencenbaugh wind generator has a 12' diameter (three 6 foot blades), each blade 5" wide (4.5" @Chord at 3/4R), with a MAX RPM of 290-345.
       I will definitely taper the holes, probably an inverted cone 3' top descending to a 4.5' below. The inverted "T" sounds more effective, but more costly, but will consider that option.
       I'm on the west coast, in a temporate zone that doesn't get much frost at all, so that shouldn't be a real issue for curing concrete.
       Thanks again for all the replies. Joe

[ChrisOlson]

      Chris, MaryAlana, thanks for the replies- Chris, a special thanks for the comment on "horizontal force" of the spinning blades. I would appeciate how you came to that specific "500 Lbs." number? Can you quantify that with your equation? I know there are formulas for "lateral thrust", but I am not aware of them.

It was just a rough guess.  2.13 kN (479 lbf) is the horizontal thrust load my 3.5 meter turbines produce on the tower structure at maximum output (3.0-3.5 kw) @ 90 mph wind speed.  That number takes into account not only rotor thrust, but also coefficient of drag and thrust centerline in relation to the yaw assembly.  So I used 500 lbs as a rough example number.

As far as calculations - yeah, you can calculate until your face turns blue and you won't even be close.  There's calculations in various books and whatnot that can be used for a guide.  But if you want to get an engineering "stamp" or certification on your tower for a particular turbine you have to provide an actual tested number.  You can only get that from the manufacturer of the machine, and only if they have tested it specifically to get the engineering certification on the tower for it.  I am not familiar with your turbine model, so you would have to get the actual figures from the manufacturer.

As an additional sidenote - the other figure you would need for a certified tower and foundation is the Critical Overturning Moment of the machine - this can be calculated from rotating mass in the machine, total mass in the machine, knowing the offset from the centerline of the tower's/turbine's yaw assembly, and it is calculated with the rotor running unloaded at your design survival wind speed (usually either 90 or 134 mph), with maximum braking force from the machine's braking/overspeed control system suddenly applied.  Your manufacturer should also have that figure handy.
--
Chris

[doubledipsoon]

Yeah Chris, a "moving" equation is always hard to track into stable math. That's why I've always ossilated towards "low tech" applications.....I did have one more question, since we're brain-storming. Should I point one leg towards the prevailing winds, or two? Most of my wind (6 hrs of 25 mph winds per day) comes from a specific direction. In my limited but intuitive calculations, I concluded that one leg should face the wind.....Any comments or am I overanalyzing again? Joe

[ChrisOlson]

You're pretty much over-analyzing on that one because the wind is a fickle thing.
--
Chris

[Royalwdg]

One of the most likely places for a failure on that three legged tower is when the wind pushes against two legs and one is straight back holding everything from crumpling over.  So make sure that the lowest section has enough bracing to avoid slenderness ratio issues.  I have charts showing wind load on all the diameters of wind turbines at verying wind speeds.  I'm seeing approx 1000lbs of force at 40 mph.  You have about a mechanical advantage of about 6.5. It's like a big crow bar trying to lift that concrete block out of the ground.  So 6500 lbs lift is less than 7300 lbs of concrete. You have a little safety factor but not that much.  The ground will also give you some resistance.  You don't need as much rebar as previously stated.  Just make sure your anchor reaches the bottom of the concrete.     Dave Moller

[Mary B]

Maybe this will hel Rogn SSV N tower is used for wind power http://www.rohnnet.com/rohn-ssv-self-supporting-towers tower base design at the bottom of the page

[doubledipsoon]

      Dave, thanks for the reply....Yeah, I copy with what you said, about it being detrimental having two of the three legs face the wind, and having the third (back-lying) leg hold up the lateral pressure. I did metriculate on this specific situation, and (in my genious opinion) concluded that one leg should "FACE" the wind, with the other two legs supporting the lateral blade pressure on the tower. Now, one might think that this would only work if the wind consistently came from one specific direction...Well, it does. I've been doing wind readings here for a decade and 95 % of the time the wind comes "from there". Maybe this will reduce the "possibility" of the situation you noted.
       This particular machine governs out of the wind in speeds over 24 mph. I was under the assumption that that any reliable governing maneuver would drastically reduce blade lateral force on any tower.  I don't mean to eliminate any real risks to the tower, but wouldn't the blades in the governing position, parallel to the high winds, significantly eliminate any need for worrying about huge lateral forces in high winds? This particular Sencenbaugh 1000-14 "survived winds in excess of 117 mph with no damage whatsoever", all due to its governing tail @Rocky Flats Test Center, Boulder Colorado, 1977. Probably a bit of wishful thinking here? Joe
       

[Royalwdg]

Yes.  If the blades will pitch so there is hardly anything showing to the wind or you have a tail wagger where the whole machine turns away that is true.  But not in my own case.  My blades are normally pitched at 10 degrees leading edge forward. The fly weight governor will feather my trailing edges forward 25 degrees.  That is only 15 degrees from flat to the wind.  A machine like mine will see the bigger loads at very high winds.  Dave Moller

[doubledipsoon]

Dave, thanks for collaborating on that last point....I don't know if you're familiar with the Wincharger three-legged self-supporting tower, but I planned on bolting the bottom section of the three legs to a cemented 8 foot long 3 inch diameter 1/4" thick wall (schedule 80 ?)anchor (with "hooked" bottoms), instead of the stock anchors that match the rest of the tower legs. Is bolting a "three-sided" angle iron leg to a round anchor risky? I mean, should I look around for another set of Windcharger legs to use as anchors, to match the lower legs?  Joe. By the way, is your wind generator home built?

[Frank S]

 The primary key to a good anchorage is getting your geometry correct whether you use angle shaped anchorage or round pipes. Bolting angle iron  directly to a pipe is not generally an accepted method of connection in structural steel erection without a sub plate being welded to the pipe to increase the clamping surface area. I'll try to find some accepted and not accepted methods and post the m later
 Using pipe as the down anchorage with bars passing through it in the
concrete for  a holding tooth is fine its just the connection to the legs that yo need to pay attention 

[doubledipsoon]

Frank S, I hear what you're saying, about the hidden variables inherent in bolting an angle tower leg to a round anchor, and I'm tempted to chuck the whole idea. I do have three 3 foot sections of the old angle-shaped anchors that were cut when the tower was taken down, and I could do a "heavy duty" weld job to connect them. However, I've heard that any kind of welding to anchors is asking for trouble down the line, due to vibration, rust, bad welding, and whatever else Murphy can come up with. I'll probably have some 8 foot long, 3/16" angle fabricated to serve as an anchor. It's probably overkill, as I've plenty of Jakes hooked up to pipe anchors on redo jobs. Joe

[Frank S]

When all else fails and I don't seem to find the time to search through my archives I just go out and try to find an example of what I am talking about
 Now bare in mind this is just one of the accepted methods of lattice tower mounting.
 But this method is used on millions of High-line towers all over the world





 These are smaller towers 40 to 70 feet tall
 the smallest one has a 24 inch diameter base  about 8 feet in the ground  the larger base is 3 feet in diameter  about 10 feet in the ground the only reason I know this is I remember when they were drilling the holes
 This is a bit of overkill however power companies cannot afford to take chances it is always cheaper to err on the side of too much than too little

[fabricator]

Welding bolt pads on is a common practice, rohn towers have welded bolt pads, and then we have free standing monopoles, they have one single welded flange that supports the entire tower and turbine.
It would be a good idea to find a certified structural welder though to do the welding, and we are talking stick welding not mig welding.

[doubledipsoon]

Frank S/Fabricator, thanks for the replies, and great pictures. Unfortunately, a Wincharger Tower has a "three-sided" configuration, and can't match up to a standard right-angle angle iron anchor. I'll have to get some anchors fabricated to perfectly match the bottom legs. Bolting a pipe to the legs probably wouldn't be as optimal as I originally thought....Here's a photo of the tower I bought. If you blow it up you can see the "three-sided" shape of the legs that need to be achored down, thanks again, Joe

[fabricator]

Are you a crop duster?

[doubledipsoon]

        Fabricator, have your crops been dusted lately?.....No, I wouldn't be a crop duster if they paid me in wind generators and solar panels. This is the ad I saw on Adhuntr before if was called "Allofcraigs". It took me a year to find a Wincharger tower, and I highly recommend Adhuntr for all U.S. Craigslist listings.......Anyway this dood had a Wincharger+ a Wincharger tower, with a different biplane in the background of each of the 4 pictures of his Wincharger. When I responded to his ad, he was driving a flatbed from Sonoma County, California with a helicopter, headed back to Wisconsin.....Buying it from this character was almost as good as goin' out to Santa Fe in '89 to take down a 1954 Jake....in the snow...I'm glad the picture got you off!