I think you are both a little light on the downward pressure from the guy
cables. 1/4 phillystran has 600# of pretension. cos(45)*600*3 = 1273# per
each set of guys, assuming no wind. There is not necessarily a support
cable on a self-supporting tower.
Re: [TowerTalk] Adding guys to self supporting towers
from [Roger (K8RI)] [Permanent Link][Original]
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Adding guys to self supporting towers
From: "Roger (K8RI)" <K8ri-on-TowerTalk@rogerhalstead.com>
Date: Tue, 13 Aug 2013 02:28:53 -0400
If I have figured crrectly, the worse case compressive load
on a leg at the bottom of a trianguler tower
is equal to the product of the horizontal windloading
at the top times the factor h/[w*sqrt(3)] where h is
the height and w is the width of a face.
For example, a 100 ft windload at the top of a 50 foot
tower with 18 inch face will induce 1925 lbs of
compressive force. If a the tower is guyed at the top
with the guys at 45 degree angles, the compressive
force is simply equal to the horizontal wind load, or 100 lbs.
Much less than the unguyed 1925 lbs.
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.
The guyed tower will have the same downward load, PLUS the guy tension and
the additional transformation from horizontal forces to vertical caused by
the guy(s) his is not a simple transformation, but assuming worst case
where the wind lines up with one of the guys
If you have 1/4 inch Phyllistran at 440# tension (cos(45)*440 )*3 = 693#
additional load on the base The downard force from the horizontal wind is
another 1637# for a total of 2330#
This is an increase of slightly over one ton and probably exceeds the
capability of the lifting cable which does not have a great deal of excess
strength. Just the 693# from the guys which is less than EHS would be
pushing your luck
73
Roger (K8RI)
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