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

[Jim Lux]

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.