[TowerTalk] tower setbacks/falling trees

[K8RI]

On 2/4/2012 9:53 AM, Jim Lux wrote:
> 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.
>
> Now if a 100' tall tree on my own property, falls  down on my neighbors'
> house, the neighbors'  own house insurance covers the damage.   If the
> neighbor does not have insurance, he is outa
> luck. My insurance does NOT cover my neighbors' home.  Same deal with my
> tower.
>
>
> --
> 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.

I've never heard that before and it'd be pretty difficult to get a tower 
made of identical sections to break at a predetermined point.
>
> The question would be whether it would fly in a regulatory context. It's
> well known that tall skinny freestanding
The keys are tall AND skinny AND free standing. That does not include 
most ham towers and you rarely find tall, skinny, and free standing 
apply to the same structure unless a guyed tower loses its guys. Then no 
one knows where it's going and whether it'll stay in one piece or not.  
"I'd guess" that a 25 or 45G would stay in one piece...maybe.  Actually 
if it has a lot of mass on top, then I'd expect the tower to fold. A 
tower tends to accelerate at 32ft/sec^2. all along its length  Due to 
the base pivoting the top of the tower can not keep up with the bottom 
because it has farther to go in the same time while accelerating at the 
same rate and it tends to bend back out a ways from the base if the 
tower is tall enough to have enough mass to cause the tower to bend of 
break.

> 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)
If a 100 foot ROHN 45 lost the guys on one side it'd likely stay in one 
piece. If a tree fell on one side who knows what it'd do.

>
> The tower vs tree thing is more about "manmade" vs "natural feature"..
> and, I suspect that if you had a big tree with obvious defects in it and
> it fell on someone else's stuff, you'd wind up with liability.  All what
> a "reasonable person" would have done to mitigate the obvious danger.
Setbacks are considered a safety issue and I don't know of any that have 
been turned over and are more often in zoning regulations.

73

Roger (K8RI)