| I am an electrical engineer and probably should know better.... live and learn.
I constructed a 40 foot tower for my wind turbine using supplies from Home Depot and Lowes (first clue?). I used schedule 40 1 inch pipe staggered inside of 1.25 inch schedule 40 pipe with couplers made from 1.5 inch schedule 40 pipe (turned on my lathes to slip over the 1.25 inch pipe).
The 1 inch pipe I butt welded together, slipped the 1.25 inch pipe over and butt welded and then welded couplers every place either the 1 inch or 1.25 pipe joined.
You would think that would be plenty strong. Here is the kicker... I studied the mechanical properties of the pipe... ASTM A53A and the modulus of elasticity was over 30,000 PSI. I added the guy wire connection points using .375 inch solid bar that I bent to form loops and welded that to the 1.5 inch couplers just below the blades and another 12 feet down. I used 5/16 inch guy wire on the top and 3/16 guy wire on the bottom connector. I raised the tower for the first time last Thursday and the pipe looked like a snake..... bending and bowing.
It was at this point a neighbor (oil field roughneck) stopped by to see what I was up to. After some discussion he enlighten me... I did not use structural steel and while the mechanical data was correct I had completely misinterpreted the data.... there is a huge difference between "wall strength" and "rigidness" (flex strength).
I am now adding 1 x 1 x .25 inch angle iron along the length of the tower pole (front and back) to increase the flex strength (Just stubborn I guess, I should have started over with the correct materials).
My anchors and base are all made from 1200 lbs of cement each poured 12 inches thick over cages of rebar I welded together (my anchor eye bolts and the bolts for my pivot are welded to the cages). {We see 100 mph winds on occasion and 25 mph winds very frequently... almost daily). I do try to over engineer everything (drives my wife crazy) but the point is ignorance is expensive....
It was at this point I discovered a good place to purchase structural steel: Metal Distributors in Ft. Collins, CO. It's an hour and half from the farm but worth the drive. (Metal Distributors may be found on the web under Colorado Iron and Metal in a Google search)
If I manage not to pull all of my hair out or jump off a cliff in frustration (difficult to do out here in the plains) the next tower should be straight forward :)
The advice from my 11 year old daughter: "Try, Try again"
At this point, I would have saved over $100 dollars by going with the more expensive structural steel pipe right from the get go.
Ignorance & Arrogance are quickly countered by reality. I am eating my share of humble pie today.
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