Bill:
I agree with your observations concerning the guyed tower and potential
failure scenarios...
The freestanding tower if engineered and installed correctly and with a
constant cross section will fail at the base not 15 feet up. A cantilever
structure will always have the maximum moment and shear at the fixed support
point, i.e., the base in this case. How the structure behaves after the base
fails is another matter and is not quite linear in terms of cause and
effect. Worst case is that it falls full length on the ground.
For Bob: I think there is a Tower Erectors and manufacturer's association,
something like NACE or similar. They may be a viable source of tower failure
forensics and behavior.
Hank Lonberg, P.E. / KR7X
-----Original Message-----
From: Bill Coleman [mailto:aa4lr@arrl.net]
Sent: Thursday, February 22, 2001 11:22 AM
To: Bob Thacker; towerTalk@contesting.com
Subject: Re: [TowerTalk] Tower Failures
On 2/21/01 16:09, Bob Thacker at k3gt@pgh.net wrote:
>Am working with the local township on drafting new ordinances and would
>like to know if there are any concrete studies showing that a tower will
>fall within a %age of its height. Have heard that it is either 40% or
>within the guy radius. Since we will be addressing free standing towers any
>info there would be appreciated. Also sure that plain verticals will be
>addressed since yours truly has already requested to erect an 80m 4 sq.
Bob, I don't have an specific studies, but I've also seen the 40% figure
bandied around for guyed towers. It does make sense. Even if a top guy
fails, the remaining guys limit how the tower can come down. Guy radius
is usually 80% of height, so 40% is certainly within 80%.
For freestanding towers, while it is physically possible to have a base
failure that results in a 100% fall, most failures like that are unlikely.
Consider how trees fail. If you've ever seen downed trees after high
winds or a tornado, trees rarely fail right at the ground. (Unless the
soils gets so soft the roots just squish right through) Instead, trees
tend to fail 10-25 feet up, with the mean being somewhere around 15 feet.
That's the high stress point for a freestanding structure.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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