99% Invisible

Episode 52- Galloping Gertie

Even during the construction of the original Tacoma Narrows Bridge, the deck would go up and down by several feet with the slightest breeze. Construction workers on the span chewed on lemon wedges to stop their motion sickness. They nicknamed the structure Galloping Gertie.

The original Tacoma Narrows Bridge design by Clark Eldridge was pretty conventional for a suspension bridge, but it was later modified by Leon Moisseiff to be slimmer and more elegant. The most notable change was that the 25 foot lattice of stiffening trusses underneath the bridge on the original drawings, were replaced with 8 foot solid steel plate girders. The new solid girder along the side in Moisseiff’s design made for a much lighter and more flexible bridge— it also caught the wind like a sail— but they didn’t know that. Moisseiff’s design was also 2/3 the price of the original Eldridge design and that fact ultimately won the day.

Motorists who used the bridge found out first hand why it got the name Galloping Gertie, and during the four months while the bridge was open, many traveled from far away just to ride the undulating waves as they crossed high above Puget Sound. The thrill ride didn’t last long.

On November 7, 1940 stiff winds caused the road deck to twist violently along its center axis. The center span endured these brutal torsional forces for about an hour and finally gave way.

The collapse of the twisting suspension bridge is one of the most dramatic images caught on film.

I talked to John Marr from the seminal zine Murder Can Be Fun for this story and I’d like to give a shout out to Alan Bellows of Damn Interesting for independently suggesting Galloping Gertie as a show topic and publishing a great, much more detailed account of the disaster on his site.

Special thanks to Benjamen Walker for the audio of Kathryn Schulz. That interview originally aired on his show Too Much Information in the episode called “Mistakes Were Made.”

Thanks also to Steve Burrows (from the Pyramids episode) who talked me through the basics of aeroelastic flutter and vortex shedding. Those explanations for the bridge failure were a little too unwieldy for the episode, but I’m glad I now know it!

Source: SoundCloud / Roman Mars