[TowerTalk] Tower Concerns

[Dave Armbrust]

It has been suggested that I ignore the bracket as it could fail and design
it as self supporting.  So I ran the numbers.

Here is the conclusion I can make regarding Self Supporting Rohn 45g tower
in a 110 MPH based on the best information provided to me by Rohn and
others.  Assuming 9.7 sf of antennas centered at 4.7 ft on a 2" mast the
highest I can go and not exceed Rohn specifications is, drum roll please, 10
feet!

A 20' tower with mast and antenna totals to 16,735 ft-lb (this is not
counting the rotor or the four feed lines.  This exceeds Rohn 11,400 ft-lb
limit by 47%.  This is taking into account the varying wind loads at
different heights.  Plus I need to pour about 3-4 yards of concrete to keep
this massive 10 foot tower vertical!  Plus I should really hire a PE before
I consider doing this.

Of course this 10' tower is not even tall enough to reach my 15' bracket!

73--
Dave Armbrust - AE4MR
ARRL WCF Section Manager
(941)378-1701 Fax: (941)929-0040



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