Galloping Gertie: The Bridge That Taught Engineers Humility
Near Tacoma, Washington
On the morning of November seventh, nineteen forty, a forty-mile-per-hour wind was blowing through the Tacoma Narrows, the strait that separates Tacoma from the Kitsap Peninsula. The bridge that spanned the narrows, which had opened to traffic only a hundred and twenty-nine days earlier, began to do something bridges are not supposed to do. It began to dance.
The Tacoma Narrows Bridge was, at the time of its completion, the third-longest suspension bridge in the world. Its designer, Leon Moisseiff, had given it an unusually slender roadway deck, only eight feet deep, supported by solid plate girders rather than the open trusses that would allow wind to pass through. The bridge had been undulating gently since construction, earning the nickname Galloping Gertie from workers and locals who drove across it for the sensation of the rolling motion.
On November seventh, the motion became something else. The bridge began twisting in a standing wave, the roadway rotating on its axis at the midpoint of the main span. At around nine forty-five in the morning, a car and a delivery truck were left on the deck.
The occupants got out and walked, clinging to the cables, as the pavement beneath them pitched and heaved. The car of newspaper editor Leonard Coatsworth held a three-legged cocker spaniel named Tubby, who belonged to his daughter. Tubby refused to be led from the car and went down with the bridge when the main span collapsed into Puget Sound at approximately eleven in the morning.
The engineering failure was later identified as aeroelastic flutter, a resonance phenomenon in which wind energy feeds back into the structure's own oscillations, amplifying them without limit. The bridge was not merely shaking in the wind; it was drawing energy from the wind and converting it into motion, a self-reinforcing cycle. Moisseiff's elegantly slender design, which had seemed like an aesthetic triumph, had removed the structural mass that would have dampened the resonance.
The collapse of Galloping Gertie became one of the most studied engineering failures in history. Footage of the twisting bridge was used in physics classrooms for decades. A replacement bridge, using the original towers and cable anchorages but with a much stiffer deck, opened on October fourteenth, nineteen fifty.
The debris of Galloping Gertie rests on the floor of the narrows, now designated an artificial reef.
