On Nov 23, 2008, at 11:43 PM, Richard Elizondo wrote:
> Here is the shocking sad truth:
>
> Rohn 25g section shearing strength - 2500lbs (this is the strength
> of the
> entire section, all three legs and lattice, not just that one leg
> you may be
> attaching to.
>
> So a Rohn 25g section could fail if a climber falls and the lanyard
> shock
> pack does not activate, or the climber is using a lanyard without a
> shock
> pack.
>
> Sadly enough the Rohn 45g section is not that much stronger.
However, in a fall arrest situation, it is unlikely that all of the
arrest force occurs in the shear direction. 25G has considerably more
vertical support strength. On a 200 foot 25G tower, the static load on
the base likely exceeds 2500 lbs to start.
> Solutions for the Climber:
>
> First and foremost - Never attach to the Z lattice of these towers
> for any
> reason.
If a single weld fails, then the Z bracing will deform -- that
deformation will absorb some of the fall energy. The remaining energy
will be directed at the remaining upper and lower welds. It seems
unlikely that a 6 foot fall would create so much energy as to undo
every weld on a section.
It does seem seriously unwise to attach to the top or bottom "flat"
part of the bracing. There, a single weld failure would likely allow
the fall arrest lanyard to detach from the tower entirely.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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