On This Day – 7th November

The 1940 Tacoma Narrows Bridge,

the first Tacoma Narrows Bridge, was a suspension bridge in the U.S. state of Washington that spanned the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula. It opened to traffic on July 1, 1940, and dramatically collapsed into Puget Sound on November 7 the same year. This is probably the biggest and most famous non-fatal engineering disaster in U.S. history. Throughout its short existence, it was the world's third-longest suspension bridge by main span, behind the Golden Gate Bridge and the George Washington Bridge.

Construction began in September 1938. From the time the deck was built, it began to move vertically in windy conditions, so construction workers nicknamed the bridge Galloping Gertie. The motion continued after the bridge opened to the public, despite several dampening measures. The bridge's main span finally collapsed in 40-mile-per-hour (64 km/h) winds on the morning of November 7, 1940.

The portions of the bridge still standing after the collapse, including the towers and cables, were dismantled and sold as scrap metal. Effort to replace the bridge were delayed by the United States' entry into World War II, but in 1950, a new Tacoma Narrows Bridge opened in the same location, using the original bridge's tower pedestals and cable anchorages. The portion of the bridge that fell into the water now serves as an artificial reef.

The bridge's collapse had a lasting effect on science and engineering. In many physics textbooks, the event is presented as an example of elementary forced resonance; the bridge collapsed because normal speed winds produced aeroelastic flutter that matched the bridge's natural frequency.The collapse boosted research into bridge aerodynamics-aeroelastics, which has influenced the designs of all later long-span bridges.

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