Re: Foundation for Windtower
Thank you for the info and formula. I don't yet have a turbine or tower, so I'm missing numbers for the formula. At this point I am really just putting out feelers to see "whats got to be done when it's time to do it".
Is your spreadsheet in such a form that you can email it to me?
----- Original Message -----
To: Fred Thurlby
Sent: Tuesday, November 26, 2002 5:47 PM
Subject: Re: Foundation for Windtower
--- In awea-wind-home@y..., "Fred Thurlby" <thurlby@p...> wrote:
Perhaps my question should have been a little clearer.
Build codes aside (I'll look into that when the time is a little nearer), is there a general rule of thumb, ie: how many feet down
should the concrete foundation approximately go for every foot of tower ?
For self-support lattice type towers:
The general principle is to calculate the thrust on a turbine, locked, in 100 mph winds = maximum thrust.
No pitching etc = maximum drag in the wind. Knowing the lbs and the height, multiply and get foot pounds of moment at the base. Using one side of the tower as a base or pivot, divide the moment by the number of feet to the upwind leg from the pivot axis. This will be the force pulling up on that leg. Using that up force, calculate what the concrete and dirt forces must be in the down direction to stop the lifting out of that leg. Concrete and dirt are about the same weight, that is about 3000 lb per cu yard. The leg usually has a welded cross piece of about two feet in length that is imbedded in the concrete crosswise. All the dirt in a cylinder above the concrete is treated as down force. This applies directly for a three-leg tower, The force is split for a four-leg tower. I have seen four-leg towers crumpled when without adequate X bracing horizontal between the legs. The X bracing I am talking about here is the top down view.
The leg tower holes are usually dug out much wider at the bottom for the concrete base. The lattice tower is usually fully assembled in place before the concrete is poured. We have to block and hold the legs so that the tower is vertical.
My spread sheet will take in the turbine power, at maximum desired RPM, calculate the turbine size and the tower thrust X 2 for safety.If you just tell me the radius or diameter, number of blades, and if you desire some particular drag wind, I will get back to you what the calculated tower forces are from the wind generator.
I am Orville Lynner orvlynner at interfold com
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