wind turbine footings

[Guest]

i am going to installing a 60 foot lattice tower, a free standing unit.
anyone know a place where i can get specs for how deep footings should
be, diameter etc?

thanks

 

[William P.N. Smith]

i am going to installing a 60 foot lattice tower, a free standing unit.
anyone know a place where i can get specs for how deep footings should
be, diameter etc?

Try the tower manufacturer, and/or the wind turbine manufacturer. I'd
think this would be something you'd want to buy all on one place, so
you can get the answers to these questions from the one true source.

 

[Guest]

Ya know there's a branch of engineers that don't do anything BUT
that?

so, do you know of any? or where they may be at?

1) How big/heavy is your wind generator, and how much thrust does it
put out?

2) Are you keeping it free standing, or are you going to guy wire it
off as well?

i said it was free standing, a 3 legged lattice , 59 feet tall, base is
6 feet from each leg

3) What is the soil like? Loose and sandy, heavy clay, solid rock?

clay from 12 inches below top soil

4) What is your highest expected wind load on the tower?

i have clocked 93 mph last year at 6 feet off the ground . avergae wind
speed is 14 mph in summer winter more, i live on minnesota

All that said and asked, concrete is cheap. More is always better.
The main risk is not the tower sinking into the ground; it's the tower
catching a big gust of wind and tipping over. You have to make sure
that the leg is being held down firmer than the wind and generator can
pull sideways.

i know that, that is why i thought that someone had put one up in this
group

Just as an "in the ball park" statement, I wouldn't consider putting
less than a cubic meter of cement under each foot under the best soil
conditions.

is there a formula for how deep the holes are and how wide etc?

 

[John T. McCracken]

so, do you know of any? or where they may be at?

They congregate in the yellow pages, at least in the U.S.

JTMcC.

 

[Pike]

I would definitely go with a concrete pad for the tower and then guy wires
attached low enough to not interfere with the blades. I'm sure it would cost
1/10 th the price of a mounted pylon, but you might want visual elegance and
have lots of money.

 

[Nick Pine]

a 3 legged lattice , 59 feet tall, base is 6 feet from each leg

So each "face" is about 10' wide. Say the wind pushes on 590 ft^2, 30' up.

i have clocked 93 mph last year at 6 feet off the ground...

Pv = 0.00256x93^2 = 22 psf, with 590x22 = 13K pounds of force
and 30x13K = 390K ft-lb of overturning moment.

is there a formula for how deep the holes are and how wide etc?

You might assume the wind is trying to lift one windward foot, 9' away
from the line connecting the leeward feet, so the windward foot has to
withstand P pounds of uplift, where 10P = 390K or P = 39K pounds, about
260 ft^3 or 10 cubic yards of concrete, or soil over a deadman.

Nick

 

[[email protected]]

I worked for a Co. that installed some of the wind turbines
in the San Gorgonio Pass(Palm springs, CA) as well as the
Altamont Pass(South of San Francisco).

The tower is very similar to what we were putting up.

Soil was blowsand over gravel type stuff. The footing was
21' x 21' x 3'.

The 21' pad came about as the direct result of a 15' sq pad
being pulled completely out of the hole when a turbine "ran
away" in the wind at Altamont. Failed to feather
blades/rotate the head is my guess.

Near 50 cubic yards of mud.

No problems with the larger pads.

gary

 

[Walter Daniels]

[email protected] (Nick Pine) wrote

Isn't that for an enclosed tower? This one is lattice, isn't it?
Wouldn't that greatly decrease the wind resistance?
I agree, 600 square feet of "sail" in a 90mph wind would be a bad
idea ;-).

Now, with the massive reduction in surface area of an open lattice
structure, would that be, say, 20% of that, even fifty percent to be
generous? Then, of course, you have to subtract the weight of the
tower and generator itself. One of those little whispers, not a big
weight, but say, an old Jake, that trips in at six hundred pounds all
by itself...

You should not assume _less_ than 50%. IIRC at high wind speeds, a
"lattice" is almost the same as a solid surface. In any case, once
past the "tipping" point (where weight begins pulling it over), the
weight works against you.

As Nick suggests, you need both weight *under* the tower, and a
surface to resist uplift. If you don't want to spend the money for
engineering design, plot both independently. I.e., 20' pad, and 5 ton
weight (where either would be appropriate). IOW, "If in doubt,
*overengineer.*"

DJ

I studied engineering (1980-82), and I am *not* an engineer. Nothing
above is to be taken as _real_ engineering advice. I am only an
educated amateur.