[TowerTalk] Equalizer plates - a PC conspiracy?

[00tlzivney@bsuvc.bsu.edu]

Catchy title - (equality even when not equal is clearly Politically Correct)

Now the meaty subject....

I'm sure many are using Rohn equalizer plates.  I think there is an inherent
flaw in the idea.  Follow.

The Rohn catalog shows a number of towers with unequal sized guy wires and
unequal static tensions using Rohn anchors with equalizer plates.  For example,
5/16", 1/4" and 3/16" with appropirate 10% initial tensioning.  The equalizer
plate will pivot in response to any change in tension.  Assume a big wind -
one near the rating for the tower guying configuration.  Because a larger
guy is used on top, I assume that Rohn expects greater force here than at the
bottom on the smaller guy.  At the posited high wind force, the 5/16" guy
will put, say, 10,000 pounds of tension on the equalizer plate, which will
rotate to "equalize".  Since the holes in the plate are equally spaced about
the pivot (anchor) hole, equal force will be exerted on the 3/16" guy, far
exceeding its rated capacity.  Thus, the 3/16" guy may fail.  Now what, folks?
The equalizer will rotate, sharing the load on the remaining guys.  Now the
loads are higher on them than before (one guy missing, plus the increased
sharing on the next smaller guy from the rotation of the plate).  Catastrophe!

I conclude that if one intends to follow the Rohn suggestion of different
sized guy wires, that one should NOT use equalizer plates.  Or, put differenetly,
if you intend to use equalizer plates, one should use the same size guy
material for each guy!!!!!  

The good news, at least for hams, is that most of us do just that - use the
same size wire for each guy, partly out of laziness!

Terry Zivney, N4TZ/9
00tlzivney@bsuvc.bsu.edu

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