[TowerTalk] Re: Tower Loading
Thu, 20 Feb 1997 11:43:31 -0800 (PST)
At 02:59 AM 2/12/97 -0800, W7NI wrote:
>I think a more complete story about the 100 feet of 45G that failed would be
>extremely interesting to the listeners of the the tower reflector. What was
>on it? Ice? Wind? How many guys? Any guy failures? Torque arms used?
>Torgue stabilizer assembly used? This is the first failure of this kind
>other than really tall broadcast towers I have heard of. Inquiring minds
>want to know . . .
Stan and all,
Sorry for the delay in sending this out.
The 45G that failed had a 48" solid dish mounted at the top. It was guyed
at 30,60,90' with the dish face mounted at the 95' level. The mode of
failure was twisting caused when the dish azimuth arm broke and allowed the
dish to swing out from the tower making effectively a 48" sail at the end of
a 36" moment arm. The gusts would slam the dish against it stops.
Eventually the twisting motion weakened the zig-zags above and below the 60'
foot guy and the tower spun about 45 degrees counter-clockwise and fell
over. When the dust (snow) settled only the first 30' of the tower was left
standing. The rest was a pretzel laying within a 30' circle.
No ice, torque arms. The guys were attached using the GA45 brackets. We
classed this as a "beyond the design parameters" failure. By the way, this
was the 3rd failure of this type of dish mount....all because the az-arm
broke. We figured that one out too: dish mounts were for our old 6 gig
microwave system that used 18" open grill dishes....not rated for this
73 Gary K7FR
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