In a message dated 10/7/01 8:58:55 PM Pacific Daylight Time, kr1g@hotmail.com
writes:
> PS: also remember that a C4-XL, for example, at the top is not the same as
> one half the height.
Do you mean that it exhibits less load when it's not at the top of the
tower? The Rohn spec is for TOTAL tower loading but 90% of installations are
headload (at the top).
One of the things you need to remember is that the specs in the Rohn book
for 45G on up have DEDUCTED 8 sq.ft. for a symmetrical antenna mount (look
under "General Notes" on the tower configuration pages). This is a common
appurtenance for commercial applications so feel free to add the 8 sq.ft.
back into your tower capacity.
Also, all towers are designed for a certain amount of overhead or safety
factor so, yes, they will take more than their stated capacity. But the
overhead is quickly gone when you get a high gust over your design speed
(wind pressure is NOT linear).
Anecdotal information also indicates that 45G and 55G will take just
about anything you can throw at them. But I'll never talk someone out of
over-engineering something and general tower construction conservatism.
Cheers,
Steve K7LXC
Tower Tech
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