I have personal knowledge of several ham tower fall-overs
where the towers fell their full length.
Case 1
120 - 140 ft of Rohn 25 and several antennas in suburban back yard.
Tower fell over with antennas impacting neighbors swimming pool.
I remember seeing that the guys had only 2 clamps per
termination. (As I recall, the owner claimed 3 for obvious reasons)
Case 2
90 ft R25 with TH7 and 40M rotary dipole at top.
Guys were attached to cut off utility poles with
large bolts through the pole and 4"? square plates
on the back side. One pole sat next to a garage.
Over the years, the added water drainage from the
roof rotted the pole. The 4 inch plate pulled through
the top of the pole. Tower fell straight over into
neighbors yard.
Case 3
100 ft of R25 guyed at 3 levels. CB installer didn't
know about trolley / tram line antenna installation.
He had the owner detach all 3 guys on one side
so he could pull the antennas up. Wind came up.
He rode it down to his demise.
Case 4
40 ft of Rohn 25 on roof of building for many years
with tribander and 2L40 on top. HIGH winds came up.
Guys pulled through cable clamps and tower fell over on
roof. Suspect clamps worked loose over years of
temperature cycling. They need to be inspected and
tightened ANNUALLY, going back and forth at least twice.
Case 5
100 ft R25 guyed to equilizer plate with large SINGLE bolt
through the anchor eye. Defective imported bolt failed.
Tower laid over it's full height.
Case 6
50 ft R20 with 5L10 and 5L15 on top. Supported by house
bracked and 3/8 inch ALUMINUM guy wire with single strand
of steel in the center. NO thimbles at anchors. Wire fatigued
at anchor. Tower fell over with antenna booms penetrating
neighbors house roof.
Yes, ALL of these cases resulted from improper installation.
IMHO, GUY GRIPS are MUCH safer, and obviously easier to
to install, than cable clamps. As I have often reported, I had
2 trees fall on the top set of guys to a 130 ft R35 tower and
the guys held the trees up!
I have NEVER heard of an amateur tower (<200 ft) crumpling.
On the other hand, N4ZR makes a good argument about using
2 anchors in each direction.
All of my towers from 90 to 130 ft use 2 anchors with the bottom
two guys (30 and 60 ft) going to the first anchor spaced 60 ft
and the upper guys going to the second anchor spaced 90+ ft.
A PROPERLY GUYED tower *should* survive 100+ MPH winds.
The antennas may well blow apart. You probably won't show
this post to your building comminioner :-). Sorry.
Tom N4KG
On Mon, 06 Aug 2001 07:34:31 -0600 "Gary McDuffie, Sr."
<mcduffie@actcom.net> writes:
>
> On Mon, 6 Aug 2001 06:46:34 -0600, n4kg@juno.com wrote:
>
> > Crumpling may apply to VERY TALL towers like the
> > 1000 footers used by TV stations under SOME conditions.
> > I've NEVER seen it happen to Rohn Ham towers.
> > When the guys or guy anchors fail,
> > THEY FALL OVER, STRAIGHT OUT to their FULL HEIGHT.
>
> Again, I'm no structural engineer, but I would think that falling
> straight out would be indication of an abnormal situation. It seems
> that if it were properly guyed (with proper strength guys at each
> point), it would fold, because the remaining guys would pull toward
> the
> center. On the other hand, if a complete anchor failed, it's going
> to
> have a tendency to lay over full length.
>
> Gary
>
> ag0n at arrl dot net
> http colon slash slash mcduffie dot ws
> --
>
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