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

[GEORGE BETHEA]

Picture and initial analysis from eye witness:


http://dx-world.net/2013/oh8x-tower-collapse/

Info from February 2013... in depth look at the system and its performance:

http://g7vjr.org/2013/02/radio-arcala-visit-oh8x-finland/

73,
George



________________________________
 From: Jim Lux <jimlux at earthlink.net>
To: towertalk at contesting.com 
Sent: Tuesday, December 10, 2013 7:45 AM
Subject: Re: [TowerTalk] [MWA] OH8X 80-160 monster tower collapses
 

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.



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