[Towertalk] Inquiry - Tower Collapse/Fall/Radius Zone

[Steve Maki]

K2AV wrote:

>One thing I do NOT see often in these collapse discussions, is
>discussion of the merits of self supporting towers in these tight
>situations.
>
>A guyed tower is made of the same stuff at 0-10 feet as it is at the
>top. The guys keep it up. If the top wants to come over, suddenly
>missing a guy or two, there is hardly any stiffness to keep it in the
>vertical.
>
>A self-supporting tower is made of much stronger stuff at the bottom
>than at the top, and apparently has a VERY different failure mode. I
>have heard only one failure story on a Trylon self-supporter. (LXC,
>any tales or stats on self-supporting?)
>
>That was 50 mph winds after 2 inches radial ice. It twisted the top 30
>feet which bent over on itself. So far as I know, the bottom half of
>the tower was reused after the bent stuff was removed.
>
>If the nature of the ordinance or setback rules or size of lots are
>going to keep one down below 100 feet anyway, why not get some mileage
>out of self-supporting towers in the local rules? So many feet setback
>for guyed towers, some significant amount less for self-supporting.

My first reaction to this was "what causes guy wires to be missing,
anyway?" But trees falling, vandals, errant backhoes, etc. are all
valid concerns I guess. Guyed towers can certainly be built with any
amount of overkill desired. I think ordinances should lean more
toward engineering standards than cookie-cutter set back rules. 

>And with self-supporters you can do things like run a safety wire to
>the top to latch onto when climbing. (There are many advantages to no
>guy wires, other than causing that skinny Rohn 25 to fall.)

Huh? What prevents safety wires on guyed towers? In fact, they are
required on commercial towers, guyed or self supporting.

73,
--
Steve K8LX