> 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
> 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
> 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
> 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
> 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.
> When you consider using a gin pole, due consideration must be given not
> to how strong the pole itself is, but to how strong the attachment point
> the tower is. Obviously the forces at play when using a gin pole increase
> the length of the pole is increased, especially as the lateral forces on
> gin pole increase.
> For as easy as it is to build 25, 45 and 55 tower using proper gin poles,
> don't understand why one would want to complicate things by assembling
> 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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