[TowerTalk] Guying a Rohn TA-55

[Grant Saviers]

A good question.  As I understand EHS guys

1. The stretch is negligible and not considered in the guy analysis.  
The catenary sag is subject to the pretension and thus affects the sway 
of the tower in wind.
2. The tower section has a maximum compressive strength, it is specified 
in the Rohn spec for each type of tower.
3. In a no wind condition, the sum of the tower weight above, antenna 
etc. weights, and downward guy forces create a compressive load, which 
is maximum on the bottom section.
The guy forces sum by (# of guys per level) * (guy tension *sine(angle 
of guy to ground)) and add them up for all guy levels

So when you double guy at a level eg with the torque arm stabilizer, if 
the same pretension is used the downward compressive force doubles for 
that level.  Since you are considering the top level then the sine(angle 
with ground) is the largest of all the guy levels.  So switching to six 
1/4 EHS and 600# initial tension would yield the same compressive force 
and breaking strength at the top level. Except if the tower is twisting 
a lot, then it's not so clear.

Whether more than 1100# is ok or not needs a PE analysis of the 
structure with the antenna loads. 6600# total top 5/16" guy tension may 
be ok or not.  130mph design is "3+ sigma" out in amateur radio towers, 
best consult a pro with the sw tools to do the analysis.  My 140' R65 
tower with double guys at two levels (60 & 120') was PE specified to not 
exceed 600# pretension per guy with 6700# strength guys, 6 at each 
level, 90mph design, 110' base to anchors.

Grant KZ1W

On 1/2/2017 17:17 PM, CHARLES MORRISON - N1RR wrote:
> My Rohn 55 tower @ 130MPH requires three top guys of 5/16" tensioned to 1100 lbs each. If I use a TA-55 instead of three normal guys, what guying is required ? Ive found nothing about guying these. The assumption becomes to double up on the 5/16" guys.... It seems to me that adding three more of those heavy guys would negatively impact the capacity of the tower. So, before installation I'd like to get this answered and understand it.
>
> Thanks
>
> -Charlie N1RR
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