[TowerTalk] Adding guys to self supporting towers

[Jim Lux]

On 8/12/13 11:28 PM, Roger (K8RI) wrote:
> On 8/12/2013 5:06 PM, Richard Karlquist wrote:
>> The topic of adding guys to self supporting towers has been
>> discussed a number of times on this reflector, but I am
>> still not clear on exactly why it supposedly won't work.
>>
> You forgot to add the guy tension.
> This is a bit more simple than the analysis  that gave leg compression, but
>   if i use the right trig function...it's a rough view of the forces.
>

>
> Self supporting towers are much more complicated as they have leg
> compression that a pier pin mounted, guyed tower does not and must be
> stronger for a particular wind load
>
>

complicating all this is that for some towers, the limiting member is 
the diagonal cross braces.  They tend to be longer and skinnier, and so 
have lower buckle loads for column loading.  So while the vertical 
members might take the load without failing, the diagonals may not.

The distribution of uniform vertical load between corner tube/angle and 
diagonal is tricky: typically it's not something simple like a free 
pivot attachment, so you have to deal with bending and torsional loads 
and the relative stiffnesses of the members at that scale as well.

You need to get the engineering analysis for the tower in question and 
start looking at it in detail.