On 7/8/19 10:38 AM, Glenn Pritchard wrote:
Boy is there a lot of misinformation here.
Glenn, VA7UO
Sent from my iPhone
On Jul 8, 2019, at 10:36 AM, jimlux <jimlux@earthlink.net> wrote:
On 7/8/19 9:34 AM, Jim Thomson wrote:
Date: Mon, 8 Jul 2019 11:20:31 -0400 (EDT)
From: Wilson Lamb <infomet@embarqmail.com>
To: undefined <towertalk@contesting.com>
Subject: [TowerTalk] Fall Zone
<I wouldn't want a neighbor's tower/Yagi looming over my backyard...and I love
towers!
<The fall zone idea seems like simple good manners.
<I have been loosely involved in dropping 200' BC towers, dropped by cutting
the rods at one guy anchor, thus losing all guys on that side.
<They fell absolutely full length, with a few sections not even bent!
<I think a foundation failure (soil, bolt, gin pole) would drop a crankup to
full length.
<Is there any experience available on this?
<WL
## per software, Trylon self support towers will fail at the junction of the 4th
and 5th section..... 40’ above ground.
UST designs a weak spot.... which is midway up the 3rd section... 46.5
feet above ground.
## Never seen a pix of either tower folded over... as depicted above.
40 ft...and 46.5 ft. So dont know if their
design theory works....or not.
It doesn't have to be a specially designed weak spot. Towers tend to
bend/buckle in the middle anyway.
_
Well.. there's plenty of pictures of fallen towers out there. There are
towers that have failed due to wind loads (typically due to ice buildup
from a casual look) - free standing towers break somewhere in the
middle, or are hung up by external supports (power line transmission
towers are sort of a special case, they're free standing, but there's a
power line holding them up, or at least constraining where they fail.
Crankups have all sorts of stress concentrations - where the sections
overlap, for instance,
Guyed towers fail by crumpling up - a lot depends on what failed. If it
was intentionally brought down in a particular direction, they do tend
to lay out straight, because that makes it easier to haul away.
A guyed tower that fails because the anchor pulls out of the ground
tends to fall and break, but sometimes "lays out" and sometimes doesn't,
but there's almost always a "kink" in the middle somewhere (because of
the physics of falling).
I think also that there's a substantial difference between a 1000 ft
broadcast tower and a 100 ft ham tower. The broadcast tower is going to
have multiple guy tiers and is probably a lot more "slender" (and
flexible) than a ham tower.
Ham towers tend to have a lot of aerodynamic drag and mass at the top
compared to broadcast towers. That's going to affect how it fails and falls.
But overall, I would think a building code type requirement for "must be
at least the height from property line or structures" is a pessimistic
worst case requirement. (and would prevent a lot of commercial
structures from being built)
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