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Archive for November 7th, 2008

When the Tacoma Narrows Bridge was first opened in July of 1940 (after nearly 2 years of construction), it was one of the longest suspension bridges in the world.  Spanning the Tacoma Narrows, the bridge was nearly a mile long and its roadway rested nearly 200 feet above the surface of the water.  It was considered to be an engineering marvel, but this bridge also had a quirk…it liked to wiggle.

Believe it or not, all bridges wiggle a little…they can’t help it.  As structures that are always exposed to the wind, often subjected to moving water beneath them, and usually pushed on by lots of traffic, bridges have a certain about of “give” in them.  There’s a bridge near our home that’s a mile long called, not surprisingly, the Mile-Long Bridge (pictured here during this year’s flood with water that’s about 50′ higher than normal) and, when crossing it on especially windy days, you get the sensation of lateral motion.

But the Tacoma Narrows Bridge was different, as its motions could not only be felt, they could be seen.  When the wind was just right, the bridge would sway back and forth, sometimes as much as a couple feet, which quickly earned it the nickname “Galloping Gertie”.

Well, on November 7, 1940 (just 4 months after it opened), the bridge failed in spectacular fashion.  Steady winds of about 40mph were coming down the valley and the center span starting swaying.  Only this time, it didn’t calm down.  The undulations got worse and worse and, at 11:00am, the bridge collapsed.

Investigations would show that errors in the design, construction, and even painting of the bridge had all led to its demise.  Nearly every Physics class uses the bridge when studying the effects of wind, resonance, and standing waves (though those weren’t the ultimate cause of the failure).  Unfortunately, I was pretty terrible in Physics, so I don’t remember any of the technical stuff.

But what I do remember is the video that was shot of the collapse, and of the guy who was trying to cross the bridge and nearly lost his life.  As one of the most remarkable videos ever recorded, it’s an absolute must-see.

YouTube has it here.

And in case you’re wondering, there’s a new bridge where the old one used to be, and it’s way stronger than the first one.  It may wiggle a little, but having driven over it a couple times this summer, I can guarantee you it doesn’t shake like the first one.

Recommended Reading: Great Buildings of the World – Bridges – I found my copy at a consignment store and knew I had to have it.

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