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To: <>
From: "K8RI" <>
Date: Fri, 21 Sep 2007 15:53:17 -0400
List-post: <>

> Cheat et al,
> A year ago we were hoisting assembled sections of AB105 into place at NR4M
> using a special gin pole that Paul K4JA had crafted. Working at the 80 
> foot
> level, a little too much lateral pull was placed on the hoisted tower
> section by the ground crew to keep it from getting hung up on the existing
> tower. The gin pole had been attached to the top foot and a half of the 
> top
> existing vertical member. That vertical member folded over just below the
> bottom of the gin pole. Fortunately no-one was seriously hurt and we've

Many years ago I had something similar happen while trying to get the last 
bit of reach out of a gin pole that wasn't quite long enough for the 
commercial antenna I was trying to remove. Knowing better, but hoping for 
the best I too had atached the pole to the upper leg of the tower instead of 
below the first set of braces.  It was a windy day and the leg didn't just 
fold, it broke off, with the gin pole and commercial repeater antenna 
falling about 120 feet to the parking lot below. Fortunately when I saw it 
was going to "go" I hollered, "RUN" and no one below stopped to question 

> since gone to building 105 piece by piece or assembling large sections and
> craning them into place.
> Since then we've rather wondered if the gin pole had been attached to the
> next vertical member down (that had diagonals attached) whether the 
> diagonal
> would have proved enough additional support to keep it from folding over.
> The reason for attaching as we did was to get the most use of the 10 feet 
> of
> gin pole.

The tower leg above the braces has only a small fraction of the strength of 
a leg between the braces. Above the braces it is nothing more than a piece 
of thinwall tubing, pipe, or angle, depending on the tower. Which ever it 
is, it is far stronger between the braces. The AB105 is heavy and I believe 
uses flat strap for diagonal and cross bracing. Still the angle above the 
brace is nothing more than a piece of angle with the braces playing no part 
in the strength.


Roger (K8RI)
> When you consider using a gin pole, due consideration must be given not 
> only
> to how strong the pole itself is, but to how strong the attachment point 
> on
> the tower is. Obviously the forces at play when using a gin pole increase 
> as
> the length of the pole is increased, especially as the lateral forces on 
> the
> gin pole increase.
> For as easy as it is to build 25, 45 and 55 tower using proper gin poles, 
> I
> don't understand why one would want to complicate things by assembling 
> pairs
> of sections and working with the increased weight and need for additional
> vertical lift.
> Be careful up there!
> 73de Larry K7SV
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