The Tacoma Narrows Bridge

The Tacoma Narrows Bridge was opened to the public on July 1, 1940. Its opening had much pomp and circumstance associated with it. Great exaltation came with its opening, and immediately it became a household name in the area. But it didn't become known so quickly for what it did, or how beautiful it was, or how practical it was. No, it became known for something that bridges aren't supposed to do: wobble. Because of its unique trait, the bright became known as "Galloping Gertie".

If you've ever really looked at a lot of bridges, have you noticed how frail they appear to be? Buildings are large structures that weight a lot, but they have fully formed walls; they aren't just metal beams with open walls. Most bridges appear to be open beams all over the place. So why is that? Well, let's just say that if the Tacoma Narrows Bridge had been built that way, then it'd probably still be standing today.

You see, bridges have to be built with so many open spaces in them to allow wind to move through them. Buildings don't have that, but they are built to "sway" with the wind. The enormous Burj Khalifa in Dubai (over 2700 feet tall!) will sway six feet at the top with the wind. Buildings have to be strong, yet flexible. Bridges shouldn't move so much because you're driving at a decent rate of speed over them, so instead of swaying as much as buildings, the bridge has to let the wind pass through them.

The Tacoma Narrows Bridge was built too solidly, not allowing the wind to pass through it. As a result, the driving deck literally would wobble with the wind. It was a common attraction in the area. However, the longer it was there, the more violent the wobbling became.

On November 7 of that same year, the winds were blowing in at over 40 mph. The wobbling was the most violent it had ever been. The bridge was cleared, and in front of everyone, the bridge ended up shaking itself apart. The famous footage of the collapse was filmed by Barney Elliot on a 16mm movie camera. His film, part of which is in this video, is in the National Film Archive.



Four months after it was opened, the Tacoma Narrows Bridge collapsed because of a simple design flaw. The planned rebuilding of the bridge was halted because of the buildup to and the entry of the US involvement in World War II. The collapse of the Tacoma Narrows Bridge just goes to show that simple math can go a long way in such a large structure.