Quote Originally Posted by itsbob View Post
I thought the Sway and undulation is what brought down the Narrows bridge? Made a little too elastic..
If I remember, it was too stiff and didn't allow for wind, so when it went into oscillation it just ripped apart.
The first Tacoma Narrows Bridge opened to traffic on July 1, 1940. Its main span collapsed into the Tacoma Narrows four months later on November 7, 1940, at 11:00 a.m. (Pacific time) as a result of aeroelastic flutter caused by a 42 mph (68 km/h) wind. The bridge collapse had lasting effects on science and engineering. In many undergraduate physics texts the event is presented as an example of elementary forced resonance, with the wind providing an external periodic frequency that matched the natural structural frequency, even though the real cause of the bridge's failure was aeroelastic flutter. A contributing factor was its solid sides, not allowing wind to pass through the bridge's deck. Thus, its design allowed the bridge to catch the wind and sway, which ultimately took it down.[2] Its failure also boosted research in the field of bridge aerodynamics and aeroelastics, fields which have influenced the designs of all the world's great long-span bridges built since 1940.
Tall buildings are built to sway as well. Their bases are actually on rollers to allow the entire building to sway.