You’ve probably seen the grainy, black-and-white footage in a high school physics class. A giant steel suspension bridge twists like a piece of salt water taffy before finally snapping and plunging into the cold waters of the Puget Sound. It’s haunting. It’s iconic. It’s the Tacoma Narrows Bridge, or as the locals nicknamed it back in 1940, "Galloping Gertie."
But here’s the thing. Most people—even some engineers—actually get the "why" wrong.
They blame "resonance." They think the wind just happened to hit the bridge at the exact right frequency to make it shake apart, kind of like an opera singer breaking a wine glass. That's a great story for a textbook, but it’s technically incorrect. The real story of the Tacoma Narrows Bridge is way more interesting and a lot more cautionary. It’s about hubris, the desire for "sleek" aesthetics over boring old stability, and a phenomenon called aeroelastic fluttering that changed how we build everything from skyscrapers to the wings of a Boeing 787.
The Day the Earth (and the Roadway) Moved
November 7, 1940, started out like any other misty morning in Washington State. By 10:00 AM, the wind was whipping through the Narrows at about 42 miles per hour. For a bridge that was the third-longest suspension span in the world at the time, that shouldn't have been a death sentence.
It was.
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The bridge didn't just sway. It began a violent, rhythmic twisting. One side of the road would tilt up while the other tilted down. Imagine driving and seeing the car in front of you disappear below the horizon of the pavement, then suddenly reappear as the road banked 45 degrees. Leonard Coatsworth, a local editor for The Tacoma News Tribune, was the last person on the bridge. He had to crawl on his hands and knees, fingernails digging into the asphalt, to get to safety.
He survived. His dog, Tubby, who was trapped in the car, sadly did not.
By 11:00 AM, the steel gave way. The main span ripped itself apart. It wasn't a sudden explosion; it was a slow, agonizing death of a structure that was simply too flexible for its own good.
Why "Resonance" is a Myth (Sort Of)
If you ask a random person why the Tacoma Narrows Bridge fell, they’ll say the wind matched the bridge's natural frequency. This is what we call forced resonance.
But it wasn't.
If it were simple resonance, the oscillations would have needed a periodic force—like a troop of soldiers marching in step. The wind that day was relatively steady. The actual culprit was aeroelastic fluttering. Basically, as the wind blew against the solid plate girders of the bridge, it created "vortex shedding." These little swirls of air pushed the bridge up and down.
Here’s where it gets wild.
As the bridge tilted, it actually changed the way the wind hit it, which created more force, which created a bigger tilt. It was a feedback loop. The bridge was effectively "winging" it—literally acting like an airfoil and generating lift that it wasn't designed to handle. This is the same reason why an airplane wing will start to vibrate violently if it goes too fast. Gertie was trying to fly, but she was anchored to the ground.
The Man Behind the Design: Leon Moisseiff
Leon Moisseiff was a legend. He was the consulting engineer on the Golden Gate Bridge and the George Washington Bridge. He was the "it" guy of the 1930s.
Moisseiff had a theory. He believed that the weight of the main cables and the towers was enough to keep a bridge stable, meaning the actual roadway (the stiffening deck) could be much thinner and more "elegant" than previous designs. He wanted the Tacoma Narrows Bridge to look like a ribbon of steel.
Earlier bridges used deep open-lattice trusses. If you look at the bridge in Astoria or the older spans in New York, they have these massive, "ugly" steel cages under the road. Those cages let the wind blow right through them. Moisseiff ditched the trusses for 8-foot-tall solid steel plate girders.
It looked beautiful. It was a disaster.
Those solid girders acted like a sail. Instead of the wind passing through the bridge, it hit the side of the bridge like a wall. Even before the bridge opened, workers complained of seasickness. They’d see the road undulating on days with just a light breeze. They knew. The engineers tried to fix it with tie-down cables and hydraulic buffers, but it was like putting a Band-Aid on a broken leg.
The Aftermath and the "New" Gertie
The collapse changed civil engineering forever. You can’t find a bridge built after 1940 that doesn't account for wind tunnel testing. In fact, the ruins of the original bridge are still down there. They are now one of the largest man-made coral reefs in the world, listed on the National Register of Historic Places.
We eventually built a replacement. It took until 1950, mostly because of World War II and the fact that everyone was a little terrified of building in that spot again.
The 1950 bridge was different. It was beefy. It had deep open trusses that let the wind whistle through safely. It’s still standing today, and it’s been joined by a second, parallel span built in 2007 to handle the massive traffic flow between Tacoma and the Gig Harbor peninsula.
What This Means for Us Today
The Tacoma Narrows Bridge is a reminder that math doesn't care about your aesthetic preferences. When we push the limits of technology, we have to respect the physics of the environment.
Honestly, we still see versions of this today. When the "Walkie-Talkie" skyscraper in London started melting cars because its curved glass acted like a magnifying glass, that was a "Gertie" moment. When the Millennium Bridge in London started swaying because of the rhythmic footsteps of pedestrians (actual resonance this time), that was a "Gertie" moment.
We learn by failing.
If you're ever in the Pacific Northwest, drive across the new spans. Look down at the water. You’re driving over the site of the most famous engineering failure in history, a place where we learned that the air around us isn't just "empty"—it’s a fluid, and it has more power than we often give it credit for.
Key Takeaways for the Curious
- Aeroelasticity is King: Don't let anyone tell you it was just "wind resonance." It was a self-exciting feedback loop caused by the bridge's own shape.
- Form Must Follow Function: The desire for a "slim" bridge profile directly caused the structural instability.
- Vortex Shedding: The "spirals" of air created by the solid girders were the physical triggers for the twisting motion.
- Legacy: Every modern bridge you cross today is safer because "Galloping Gertie" fell into the water 80+ years ago.
If you really want to understand the physics, look up the work of Theodore von Kármán. He was the aeronautics expert who finally explained why the bridge fell when the civil engineers couldn't. He proved that you can't design a bridge without thinking about it like an airplane.
How to Explore the History Yourself
- Visit the Harbor History Museum: Located in Gig Harbor, they have actual pieces of the original bridge and a deep dive into the Coatsworth story (and the fate of poor Tubby the dog).
- Watch the Full Footage: Don't just watch the 10-second clip. Find the longer documentaries that show the "torsional" (twisting) mode vs. the "longitudinal" (up and down) mode. It’s a masterclass in physics.
- Check the Wind: If you're crossing the Narrows today, notice the wind socks and the massive truss system beneath you. That "clunky" look is exactly what's keeping you out of the water.
The Tacoma Narrows Bridge collapse wasn't just a freak accident; it was a pivot point in human history where we realized that the sky and the ground are more connected than we thought.