Dan:
For a RIGID vertical element (such as an antenna mast or a heavy
vertical made of thick-walled or solid tube), the force (say, 12.54 psf)
would be applied midway up the element, or at 11 feet above the ground or
tower top. (You can find the calculus for this in most introductory
mechanics text books.) The area this force is applied over is the effective
area of the mast or vertical antenna. So assuming an effective antenna area
of 3.67 sqft (the actual shadow area of a 2 inch mast 22 feet long), the
total force applied would be 12.54 X 3.67 = 46 pounds. The force would be
handlied as a force at 11 feet AGL or above the tower top. We all must take
this additional force and area of the mast into consideration when
calculating the total wind force applied to the tower system.
As for a real-world vertical that flexes in the wind, this will shed
some of the wind loading leading to a reduction in total force applied to
the vertical antenna. The actual number depends on how far the antenna
bends in the wind. But by using the non-bending answer for a rigid tube you
will be taking the conservative (safer) approach.
73 de
Gene Smar AD3F
----- Original Message -----
From: "Dan Schaaf" <dan-schaaf@att.net>
To: "Tower and HF antenna construction topics." <towertalk@contesting.com>
Sent: Thursday, February 18, 2010 3:02 PM
Subject: Re: [TowerTalk] wind load
> How does this wind loading information apply to a bertical antenna which
> is
> rigidly mounted at the base and flexes in the wind?
> In addition, if the vertical antenna is mounted on top of a 22 ft tower,
> which is anchored in concrete, how does this info apply?
> 22 ft tower is short in comparison and maybe can be considered non-movable
> and then the vertical can be seen as the same as if it were mounted on the
> ground.
>
> Dan Schaaf
> K3ZXL
> "In the Beginning there was Spark Gap"
> www.k3zxl.com
/towertalk
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