[TowerTalk] Tower Failures

[Bill Coleman]

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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