I have had several E-Mail from many individuals most of them private.
One item that I did mention is that I was using a formula from chapter 22 of
the ARRL antenna book for antenna masts. Since this calculates the wind
load I had incorrectly assumed that it could also be applied to towers. The
author has assured me that this is not the case and STRONGLY advises against
doing so. My apologies to the group if I in anyway implied that this is the
correct thing to do. The wind calculations in chapter 22 is a simple
static wind speed calculation, taken from classic theory and it does not
include the factors contained in tower design standards. The UBC uses a
different wind pressure at different heights, plus an exposure coefficient
for different terrain and surrounding structures. You will have a different
pressure on the mast, the antennas, and each tower span.
I want to also make it clear that I was seeking advise and I am not giving
it. In other words please do not try this at home.
Many have suggested different approaches including roof mounts and various
guying techniques, different antennas, Rohn 55, amount of concrete, etc. I
guess I did not make it clear that this is an tower that is already up.
While it is possible for me to make adjustments, such as height, it is not
practical to make major changes at this point.
I was hoping to get advise as to how high I can safely stack Rohn 45 without
having to hire an engineer. It appears that the only correct answer is that
I can not use Rohn 45 without hiring an engineer. The reason for this is
fairly clear and straight forward. Rohn does not publish ANY information
that I can use even if I design my tower for exactly what Rohn shows for a
guyed tower, bracket tower or a free standing tower. The reason for this is
that my county shows a 110 MPH wind rating and none of Rohn's information
goes up this high. I am to therefore conclude that Rohn does not recommend
that Rohn 45 be used in this area at least not without hiring a private
engineer.
It has also been suggested that the TT argument should cease ASAP as it will
only lead to more confusion. This is clearly not my intent as I would like
to withdraw my question at this point.
Please accept my sincere apologies.
73--
Dave Armbrust - AE4MR
ARRL WCF Section Manager
(941)378-1701 Fax: (941)929-0040
> -----Original Message-----
> From: owner-towertalk@contesting.com
> [mailto:owner-towertalk@contesting.com]On Behalf Of K7LXC@aol.com
> Sent: Saturday, January 13, 2001 4:44 PM
> To: ae4mr@arrl.org; towertalk@contesting.com
> Subject: Re: [TowerTalk] Tower concerns
>
>
> In a message dated 1/12/01 2:56:43 PM Pacific Standard Time,
> ae4mr@arrl.org
> writes:
>
> > Unfortunately my tower does not fit any Rohn tables.
>
> Okay, there you go. I don't see why you have ANY questions
> because what
> you're proposing is off the chart and not viable. Violation of
> the LXC Prime
> Directive (DO what the manufacturer says) will have catastrophic results.
>
> > There is no such thing as a Rohn table for 110 MPH wind.
>
> DUH!
>
> Cheers, Steve K7LXC
> Tower Tech
>
>
> --
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