[TowerTalk] wind load vs Rohn specs

[Tower2sell@aol.com]

Yes they are two different codes; but the projected area values listed in ROHN's catalog do not include shape factors. And for the math impaired I will give 3 examples.

Take the ROHN guyed 25G 70 mph towers and look up the 40, 50 and 60 foot towers

40' 
Round 18.4x1.2=22.08
Flat 11.0x2.0=22.0

50'
Round 17.5x1.2=21
Flat  10.5x2=21

60'
Round 16.8x1.2=20.16
Flat 10.1x2=20.2

As you can tell there is a pattern that you don't need to have the CIA decipher for you. As a matter of fact ROHN works in EPA and backfigured the flat or round for simplicity. 

Class dismissed,

Tower2sell@aol.com


>>Hi Pete,

My personal opinion is that you are correct in your
interpretation of Rohn's
loading specifications.

I found it strange that "Towers2sell" would say, " ROHN has
listed the actual
projected areas without shape factor" when you can plainly
see in any
relatively new Rohn catalog that Rohn lists TWO load
figures: one for flat
members and one for round members.  I would say Rohn HAS
listed load areas
with shape factors.

I further calculated the ratio of "round to flat" load areas
for many of the
Rohn guyed tower examples given and got a number very close
to 0.6 every
time.  So it appears that while the number "0.67" does not
appear to be the
Rohn choice, "0.60" does appear to be the Rohn choice.  This
apparently
compares to "0.67" which Pete says is Force 12's choice.  It
is really too bad
that the tower makers and the antenna makers can't seem to
settle on the same
number . . .  Frankly, I don't know enough about what the
current EIA specs
say to really know which one is more correct (today).
<<

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