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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