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Calculating wind turbine tower loads - Page 2

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Posted by Curbie on February 24, 2009, 4:24 pm
 
wrote:


Where does (1/sin(45)) come into play? (1/sin(45)) = 1.175221363

In other words, a horizontal 100 lb force wind load on a tower/turbine
will present an additional 50 lb diagonal force.

Force on guy is horizontal 100 lb force wind load x 1.414
Force on base is weight of tower/turbine + horizontal 100 lb force
wind load + additional 50 lb diagonal force

Thanks.

Curbie

Posted by Curbie on February 24, 2009, 5:26 pm
 
Ok, moron alert 1,414 = 1 / SIN(RADIANS(45))

I was so busy with the overall concept that I didn't convert degrees
to radians. (moron)

For those who are trying to follow this thread either now or in the
future.

Curbie
wrote:



Posted by daestrom on February 25, 2009, 1:04 am
 

<snip>

45 degrees converted to radians...


Uh... no, not quite right.

A 100 lbf horizontal load must be countered by the guy wire.  So the guy
wire, because its at 45 degrees, has 141 lbf tension in it.  That 141 lbf in
the guy at 45 degrees breaks down into a 100 lbf vertical component and 100
lbf horizontal component.  Of course the horizontal component is just what
we wanted to counteract the wind force (also horizontal).

But the 100 lbf vertical component of the guy wire *adds* to whatever the
weight of the windmill and tower is.  I misspoke before in saying:

It was supposed to read 50 lbf *gravity* load.  (I know a 50 lb windmill is
tiny).  But the point I was trying to make is that this vertical component
of the guy force is pulling down, adding to the load exerted on the base.

At a 45 degree guy wire angle, it just happens to work out that whatever the
side load of the wind is, the additional downward force caused by acting
through the guy wire is the same amount.  100 lbf wind load horizontal gets
turned into 100 lbf *additional* down force on the base.

And the wire tie down has a similar force.  The 141 lbf diagonal force in
the guy wire will pull *up* on the base with 100 lbf and *sideways* on the
guy (toward the tower of course) of 100 lbf.

daestrom


Posted by vaughn on February 24, 2009, 12:37 am
 

   Plus the reaction from the combined preload on the guys (depends on angle
of guys with ground) plus the total weight of mast and equipment.

Vaughn




Posted by vaughn on February 24, 2009, 4:35 pm
 
   Just a point of personal experience here:  Don't undersize your base
foundation on a guyed tower on the theory that everything else is more
important to holding up the tower.  As we have established in this thread,
most of your stresses somehow end up combining right there!

     Because of the recent spate of hurricanes here in Florida, I was
involved in the re-engineering and subsequent upgrading of a couple
communications towers so that they could survive a higher wind speed.  In
each case, the limiting factor turned out to be the foundation at the base
of the tower.   There is a point where adding or strengthening guys will not
help, if there is no way of beefing up the base foundation.

 Vaughn



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