[TowerTalk] Two Killed Erecting Tower

[David Robbins]

K7LXC@aol.com wrote:
> 
>        Even with 40 feet exposed, you'd have to hook up a cable from the top
> of the tower to your car in order to exert enough force to pull it over. One
> 200 pound climber in little wind is a pretty minor load even for this
> 'worse-case' scenario.
> 

Michael Tope wrote:
> 
> With 60' of unguyed 25G, one exceeds the Rohn spec for overturning
> moment when the winds hit ~60 MPH. This doesn't include any
> additional surface area for the climbers.
> 
> In calm conditions, I think you would have to get pretty rambunctious
> to yield even 60' of unguyed 25G. Even if the tower were perturb 3'
> off vertical, you would still need around 2000 lbs of dead weight to
> exceed the Rohn spec for overturning moment at the tower base.

both of these are of course assuming that they had installed both bolts of the
proper specs in all the legs and properly tightened them.  someone should
calculate the shear force on one of the bottom leg bolts assuming a reasonable
static side force and compare that to hardware store grade bolts.  then think
about what happens when you grab for something and jerk the top of the tower
just a bit more.  after reading the long story version i get the impression that
they had 60' unguyed and had stopped at that point because the owner thought it
was getting unsafe to go higher, and they were pulling up the antenna to put on
it.  i know you have all seen antenna raising operations where the ground crew
is pulling as hard as they can to keep the antenna away from the tower.  a full
analysis by an engineer would probably find many things wrong with what they
were doing, besides of course not following the manufacturers specs.

and along those lines, requireing engineers or professional installers wouldn't
have stopped something like this anyway.  these guys were putting up what would
have been an illegally high antenna for the purpose of communicating beyond the
legal limit for cb anyway. why would a group like that go thru a permit process,
let alone pay someone to put up a simple thing like a tower.  assuming that
rules that i used to know about in that service still apply even though they are
rarely, if ever, enforced.


-- 
David Robbins K1TTT (ex KY1H)
k1ttt@berkshire.net   or   robbins@berkshire.net
http://www.berkshire.net/~robbins/k1ttt.html

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