It was on the History channel this past week, on a show called Engineering
Blunders.

Kind regards,

Denys. . .

Denys Beauchemin
HICOMP
(800) 323-8863  (281) 288-7438         Fax: (281) 355-6879
denys at hicomp.com                             www.hicomp.com


-----Original Message-----
From:   Wirt Atmar [SMTP:[log in to unmask]]
Sent:   Saturday, 18 December, 1999 1:55 AM
To:     [log in to unmask]
Subject:        Re: Bridges Collapsing

Steve writes:

> Verrazano Narrows? It was certainly the longest suspension bridge in the
>  world for a number of years, but I don't think it ever fell down. OTOH, our
>  own "Galloping Gertie", a.k.a. the Tacoma Narrows Bridge, did its thing on
>  20 Nov 1940.

The Tacoma Narrows Bridge didn't fall down because of resonances either -- at
least not specifically induced by traffic over the bridge. Rather, in high
wind, it acted as if it were an aerodynamic wing and actually began to fly
upwards throughout much of its span. Under these conditions, it oscillated in
the same manner that a sheet of cardboard tethered to a fixed point by strong
twine would oscillate. That too is a form of resonance, but one that may have
many periodicities.

You can see a movie of the bridge's oscillations at:

      http://mecad.uta.edu/~bpwang/me5311/1999/lecture1/intro25.htm

The Tacoma Narrows Bridge was a flimsy structure in every dimension except
the one that it was designed for: vertical load. Its failure was well
expected, and as Steve says, on the 7th of November, 1940, it took all it
could. If you want to know more than you ever thought you would about the
Tacoma Narrows failure, there is a particularly nice web page at:

     http://www.engr.utexas.edu/uer/past/spring96/papers/paper_jk.html

Wirt Atmar