[TowerTalk] Adding guys to self supporting towers

[Grant Saviers]

Rick,

It was my wrong assumption that crank ups were in the question. Guys on 
the mast by the prior owner of your HDX5106 tower - very interesting!

I have a Trylon T200-80 on the ground which is rated 16 sq ft at 70mph 
then 2 sq ft at 85 mph.  Since a (85/70)^2 more wind force (1.5x) causes 
a 8x reduction in load capacity, my guesstimate is there is so much more 
tower projected area than a crank up.  Anybody have the PE calcs for a 
Trylon or something similar?

I can see that light guying would reduce sway, but what is it in the 
tower structure that is the limiting factor and effectively near failure 
at the 85 mph loading?   The legs on my tower are 16ga at the top and 
8ga or 10ga at the bottom.  The cross brace and leg fasteners are in 
shear, not tightened to critical slip.  My leg bolts are 3/8 at the top 
and 5/8 Gr5 at the bottom, 2 ea per leg joint, a clue to the forces 
involved.  My gut votes for leg hole tearout or maybe cross brace 
failures (1/4" or 5/16" bolts), the legs are stamped from 32ksi sheet 
metal.  It's not too hard to run the numbers of bolt shear vs hole tear 
out on a bottom section, and compare that to the HDX589 loads, but maybe 
the limits are elsewhere.

If guys work then can I put a 35' 3" mast with a stack out the top of my 
T200-80? ;-) ;-)   A Super Titan could do it.

Building an FEA model would be quite a project, but likely necessary to 
get an answer to your question.

Grant KZ1W



On 8/12/2013 4:40 PM, Richard (Rick) Karlquist wrote:
>
>
> On 8/12/2013 2:58 PM, Grant Saviers wrote:
>> I can't follow your analysis, so here are some numbers for an HDX589
>> from my PE analysis:
>
>> That said, I would bet on the hoist cables as the failure point if guys
>
> I should have said that my original query was not aimed at
> crankup towers.  I have no intention of adding guys to my HDX5106.
> But the previous owner of it did have guys at the top of the 24 foot
> mast and got away with it.  He only sold the tower to me because
> he wanted more height.  It was on the top of a mountain, so it
> probably saw some pretty good winds.
>
> Rick N6RK
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>