Jim: thanks much for your input...
Things vary according to locality. I have never, ever considered
earthquake or ice loads on my
towers...not going to happen.
If I *WAS" an engineer, nobody is gonna believe ME.
If you have a, let's say 60' foot of tower, there's a good chance that
it *might* fall down within
its length... if you have 195' of tower, there is ZERO chance any of it
is going to land 195' away from
the base...
73
Randy
KZ4RV
I
On 2/5/2012 9:08 AM, Jim Thomson wrote:
> Date: Sat, 04 Feb 2012 06:53:58 -0800
> From: Jim Lux<jimlux@earthlink.net>
> Subject: [TowerTalk] tower setbacks/falling trees
>
> VE7RF wrote:
> The rules on setbacks upsets me. To have a tower fall full length and
> still remain on your own property is pretty tough if a ham lived on a
> typ city lot..like 50' x 120' or similar. Freestanding towers, like
> Trylons are designed to break at the 40' level..and not at the
> base.They will not fall full length. A UST crank up is the same
> deal, they break 3 x sections up.
>
>
> --
> this brings up a couple interesting issues..
>
> 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.
>
> ### It's there, plane as day, as soon as you run the freestanding trylon
> through trylon's freebie software. Start cranking up the wind speed..until
> a single section lights up red. OR start with too high a wind, like 140
> mph,
> and a big ant on top....and several sections will light up red. Then start
> reducing
> the windspeed till only one section lights red. The results are always the
> same.
> The weak link is at the 40' level, at the junction of the 5th and 6th
> sections.
> OK, this is only for a trylon T-500 tower..which is 21" wide at the
> top...and
> 51" wide at the base. Other model trylons will appear to break higher
> still,
> like on a T-400. The point is, they will never break at the base. We are
> not talking
> about a guyed rohn 25/45/55 tower.
>
> ## on the detailed eng info on my UST HDX-689... you can clearly see from
> the eng
> analysis, that the weak point is the 3rd section up from the bottom. Sure,
> they could have
> strengthened that section easily, but then the break point would then be the
> 2nd section from
> the bottom. They don't want them to fall full length. Now all of this
> only applies to freestanding
> tower's whose base is a lot wider than the very top. Sure, you can free
> stand rohn 25/45/55/65G
> per rohn specs, but those towers will break at the base...and will fall full
> length.
>
> ## they don't advertise the weak point in any of these tapered, freestanding
> towers, but it's
> readily apparent when you use their software to calculate wind speed
> survival. In the UST case,
> it's clear that the 3rd section up from the bottom is far more stressed than
> the sections above or below it.
> City hall eng's agreed, and bought into it.
>
>
>
> The question would be whether it would fly in a regulatory context. It's
> well known that tall skinny freestanding things tend to break somewhere
> when falling (chimneys, pencil points), but I don't know that it's
> something that can be convincingly "designed in" in a way that will
> cover ALL circumstances. If the tower is strong enough, it WILL fall in
> one intact piece. (e.g. 200-300 foot trees fall over without breaking
> in the middle)
>
> ## with tree's..the roots are always the weakest point. They uproot
> in high winds. 200' tree's are not encased in 40 yards of concrete.
> Tree's are bad news. About 11 years ago, we had 3-4 days of heavy
> rain, followed up with a huge wind storm. Loads of tree's came down.
> Tree's in the middle of a forest have weak root systems vs
> tree's at the outer edges, and exposed to the full force of the winds.
> Once developer's remove the outer peripheral tree's..the remaining
> inner tree's are always failure prone.
>
> later... Jim VE7RF
>
>
>
>
>
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