[TowerTalk] tower setbacks/falling trees

[Jim Lux]

On 2/4/12 9:37 PM, Gene Smar wrote:
>
> ----- Original Message ----- From: "Jim Lux" <jimlux at earthlink.net>
> To: "towertalk" <towertalk at contesting.com>
> Sent: Saturday, February 04, 2012 9:53 AM
> Subject: [TowerTalk] tower setbacks/falling trees
>
>
>> VE7RF wrote:
> SNIP
> Freestanding towers, like
>> Trylons are designed to break at the 40' level..and not at the
>> base.They will not fall full length.
>>
> SNIP
>> You say designed to break at a particular point. I hadn't seen that in
>> any of the drawings I've seen, but then, I wouldn't think they would put
>> a dashed line and arrow in a bubble saying >Break here. But it is an
>> interesting concept.
>>
> SNIP
>
> TT:
> The taller Trylon Titan towers (sorry for the alliteration) are
> constructed of two gauges of steel. The upper, smaller sections are
> thinner gauge while the bottom, larger sections are heavier gauge material.
>
> If you were to use Trylon's software for determining the safety factor
> for a given tower http://www.trylon.com/lightdutytowers/towercalc.asp ,
> the results would show that the tower would run out of safety factor,
> i.e., fail, where the thinner material joins the heavier material. This
> is usually about mid-height for the assembled structuree.
>
> In other words, these towers will bend roughly in half when they fail.
> Try the software with some fictional antenna loads to see for yourselves.
>
>

Very slick web aoo..

However, just because the failure point in a windloading situation is 
halfway up the tower doesn't mean that it will fall neatly folded up, 
which was the original issue: setback and whether it's reasonable for 
the locality to require that you have enough land for the tower to fall 
straight out without crossing a property line.

I can see someone spending a sufficient amount of engineering analysis 
time and perhaps coming up with an analysis that would make the local 
authorities approve a waiver, but I think it would be an uphill battle.

My experience on seeking waivers in general is that as soon as your 
analysis starts to get complex and require a fair amount of 
understanding of underlying principles, the odds of approval go down.