[TowerTalk] Wind Calcs for a U.S. Towers MA-40
Alan C. Zack
k7acz at cox.net
Mon Mar 1 18:32:40 EST 2004
I have run into a situation with my Building Dept in my attempts to
get a building permit for a U.S. Towers MA-40. I have moved to a
countryside QTH and wish to put up a small tower. The city building
code allows me to have a 45 ft tower with no variances. Over 45 ft I
would need a variance.
I choose the MA-40 because it will crank down to 21 ft and can be
folded over at the base to work on the antenna. It has a freestanding
base. My yard is not very large and so the need for the crank down.
I would rather not climb the thing and so the hinged base. I don't
have room in the yard for guy wires. The MA-40 tubular tower seemed
ideal for my situation.
Now the problem. I took the U.S. Towers drawings and wind calcs to my
building dept. U.S. Towers originally submitted wind calcs under
UBC-97. The Bldg Dept wanted IBC-2000 calcs for 90 MPH. The U.S.
Towers PE states IBC-2000 wind calcs are that it can handle a 3.5 sq
ft antenna at 70 MPH, but at 90 MPH it cannot even support itself at
that high a wind. I can live with the 3.5 sq ft antenna by using a
Cushcraft MA-5B to keep a small, clean tower and antenna. But what do
you do when a self supporting tower can't handle a 90 MPH wind calc?
Is the 90 MPH requirement unreasonable? Can anyone suggest another 40
or 45 ft crank-up tower with a hinged base that would pass a 90 MPH
TIA for any ideas.
Amateur Radio Station K7ACZ
Las Vegas, Nevada, USA
Quality Engineer, The Boeing Company, Retired
Aviation Chief Warrant Officer, U.S. Coast Guard, Retired
U.S. Coast Guard, Always Ready, Always There
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