Ok, here's my current headscratcher: Putting up 7 sections plus a flat top
section of 45G. Book says guy at either 29' & 61' (70 ft) or 35' & 71' (80
ft). After sinking 4' or so of the first section in concrete, and adding the
8' flat top section, the thing should be about 74' tall at the thrust
bearing, so I guess I'll consider it a 70' tower for guying purposes. I'm
considering things I can do now that will make it easy someday to add 3
sections to this thing to get it up to 104'. Guys for a 100 footer are
listed at 31', 61', & 91'. Clearly, using the 70' guy pattern at 29' and 61'
would make adding 3 sections and a third guy at 91' a reasonable thing to
do, except for the distance from the base of the tower to the guy anchors,
which is what has me worried. The question is: Structurally, is it a bad
thing to put the guys for the 74 footer at the right distance from the tower
for a 100 footer now? If I did, that would put the guy anchors at 80'
instead of the 56' specified, which is a pretty hefty distance change.
Obviously I'd like to avoid putting in three more guy anchors at 80' later,
if possible. In line with this possibility, I am using Rohn anchors with
three-hole equalizer plates. I know putting guy anchors CLOSER than specs is
a very bad idea due to the added leverage and downforce they put on the
tower during high winds. Is there a bad effect from moving them further
away, say from 56' to 80'? Common sense tells me the stress on the tower
goes down as you move the guys further out, but I suppose there's a
practical limit due to sag and who knows what else. Also, I note that Rohn
always specs guy tension at 600# for the top 1/4" guy, and 400 for the
remaining 3/16" guys, no matter what the tower height (at least from 40' -
160'), so tensioning doesn't seem to be a problem either way. I'd just move
the 1/4" guy to the 91' point, add some length to it, and tension it at
660#.
Sorry for bothering you guys with questions like this but this is my first
"full-size" tower, and the Rohn data sometimes isn't all that helpful,
especially if you want to vary some parameter. BTW, this is NOT important
enough to me to spend $1500 for a PE to study it, so if it's a bad idea just
say so. Thirty feet ain't that big a deal to me as far as the yagi goes, it
would just help me out on the lower band wire antennas.
Thanks,
Jerry W5KP Mustang, Oklahoma
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