Larry Schimelpfenig wrote:
> 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
> 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.
>
> 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
>
Yes, be careful! Also, use the right gin pole for the job, attach it
among the tower braces, and never lift more than one section at a time!
People have been killed while attempting to take shortcuts on tower
construction.
If you ever watch a commercial tower company erecting a tower, you might
notice that the gin poles they use are sometimes twice as long as the
sections they're lifting, with more than half the gin pole attached to
the tower. One guy I know used 40 feet of Rohn 25G as a gin pole for
small jobs, and 55G for the big jobs.
Ethan (kc8hes)
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