[TowerTalk] Climbing and working on Rohn 25g/45g towers -

[Bill Coleman]

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 at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901