[TheForge] Tacoma Narows bridge

[jerry Frost]

Wow, you have a good memory Mike, I used to have one of those but don't
remember what it was like.

Thanks for the link, that was some good reading. Guess I got sucked in eh? I
remember the effects of wind blowing over and past objects and the ? ?
Street effect. There is a majority of blowing air is drawn to one side or
the other. The Bernoulli principle describes how the pressure will drop on
the side with the heavier flow. The other is subjected to a higher pressure
in comparison and the differential causes the structure to deflect.

I remember this described as part of the driving force causing the
oscillation of the TNB which was then "explained" as a wind driven resonance
failure. 

They did get the narrow web reinforced stiffeners part right but IIRC didn't
mention the broken suspension cables. The really long narrow roadway made
for a high aspect wing too. 

Good grief I'm off reminiscing about bridge design. I guess I worked for the
bridges and foundations section of design too long eh? Resonance can be a
problem for bridges it's just not what got Gertie. I'd picked up on the more
accurate descriptions of what happened but sometime after posting that bit
to Theforgelist. 

Dad and the brothers used to cross Gertie when she was oscillating but were
elsewhere when she fell. I thought part of Dad's tales were an example of
creative memory till he and my Uncles got together and started talking about
who crossed the highest humps. They used to say Gertie was humping the sound
when polite folk sais she was galloping. Boys will be boys you know.

Thanks again Mike that was a good read I picked up a lot.
Jer

-----Original Message-----
From: TheForge [mailto:theforge-bounces at mailman.qth.net] On Behalf Of Mike
Spencer
Sent: Friday, December 25, 2015 10:15 PM
To: theforge at mailman.qth.net
Subject: [TheForge] Tacoma Narows bridge


A long time ago (28 Jun 2002), Frosty posted a piece about the Tacoma
Narrows bridge failure.

I see that there is some revised science about how Galloping Gertie went
from undulating mode to twisting mode and ultimately disintegrated.
"Resonance" is the wrong concept.  The right concept isn't a great deal
different practically but is based on a different principle of physics.

    http://motherboard.vice.com/read/the-myth-of-galloping-gertie


Not smithing-related but Frosty, at least, had yarns from his Dad about
crossing the bridge before it finally failed.  Metal- and
engineering-related at least.

Happy Solstice, Merry Christmas, Happy New Year and good winter to y'all. 


- Mike

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^
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