My problem was not realizing that the first chart was for building bracketed
towers. Since that results in a much higher wind load rating it would be
interesting to know how much wind load figures improve if you use 3 guys on a
70' Rohn 45 tower, e.g. every 23 feet.
Steve, If nobody in the our club has a recent catalog I'll send you $5.
My concern about torque is not the twisting torque on the mast but the bending
moment on the mast and then on the tower. Maybe it is not a concern. I am not
worried about the mast bending since it would be 15' of 2" OD 3/8" wall
chrome-moly.
Concerning subtracting 8 sq. ft., is that 8 sq. ft. a round member spec or a
flat member spec? If it was a round member spec then I would have to convert
it by multiplying .6 or .67. (I see a conversion factor of .6 in the notes on
the bracketed tower page and .6 works for converting the flat member numbers to
round member numbers but Chad mentioned a factor of .67.)
The notes on the guyed page say that the tower design includes a 1/2" and 7/8"
transmission line on each of the three faces. Ours will only have two
(probably .5 inch) so it appears that I can also subtract the surface area of
the missing 4 lines (1 1/2" line and 3 7/8" lines), i.e. ( 70' * (1/2 + 3 *
7/8) / 12 ) * .6 ) = 10.9 sq.ft. But that assumes that wind load (coax) along
the side is the same as an wind load (antenna) at the top, which probably isn't
equivalent. Does anyone know how much is the right amount, if any, to subtract
for the unused coax?
73, Pete ws4g
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