[TowerTalk] [MWA] OH8X 80-160 monster tower collapses

[john at kk9a.com]

The whole tower rotated, harmonic oscillation may have been the
destructive factor. It would definitely be nice to use star guys on a
structure like this.

I wonder how well the 160m yagi worked compared to a large vertical array.

John KK9A


To:	towertalk at contesting.com
Subject:	 Re: [TowerTalk] [MWA] OH8X 80-160 monster tower collapses
From:	 Jim Lux <jimlux at earthlink.net>
Date:	 Tue, 10 Dec 2013 05:45:50 -0800

On 12/10/13 5:34 AM, Djordan (personal) wrote:
I wonder what the original design spec was for the system 75mph or 100mph...
Wonder what the cost differential would have been to raise the spec 25 mph.



On a large system like this, often times the limiting aspect/failure mode
is not a simple strength to resist aerodynamic drag effect, but some
interaction, or a dynamic effect.

The Tacoma Narrows bridge did not fail because it wasn't strong enough. It
failed because it wasn't *stiff* enough and the design had significant
wind induced torsional loads. One might say that the "Q" was too high,
although the aerodynamic design was also such that the wind excited the
oscillation in the first place.

Until some sort of failure analysis is done, we don't know if perhaps
there was a failed component, etc. That is the design accommodated the
expected loads, with a factor of safety to account for manufacturing
variability, but it was that non-zero probability of failure that bit
them.