Tomorrow marks the 68th anniversary of the collapse of the Tacoma Narrows Bridge. The bridge is famous (or possibly infamous) because of the amazing oscillations of its main span which led to the collapse. You can watch the bridge's final moments here. It's a little queasy-making to watch a huge structure of steel and concrete bouncing and flexing like a Slinky.
What caused the bridge to shimmy like that? Wind. Not some incredible super-hurricane, but just a strong breeze blowing down the Narrows. The wind made the bridge shake, just a little bit at first. But the design of the bridge and the force of the wind created what's called forced oscillation -- the same phenomenon that lets a kid on a swing soar higher and higher by pumping his legs with each swing. The force of the legs isn't very great, but if the kid times it property, the pushes build up. The same thing happened to the bridge, on a much more catastrophic scale.
A more comprehensive analysis of the bridge collapse can be found at the somewhat demoralizingly-named Failure magazine web site.
The only casualty of the disaster was a cocker spaniel.
Comments