Tacoma-Narrows Bridge Construction Collapse 1940

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Originally a public domain film from the Library of Congress Prelinger Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
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en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)
Wikipedia license: creativecommons.org/licenses/by-sa/3.0/

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. The bridge's collapse has been described as "spectacular" and in subsequent decades "has attracted the attention of engineers, physicists, and mathematicians".[1] 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 damping 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. Efforts 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...

Because planners expected fairly light traffic volumes, the bridge was designed with two lanes, and it was just 39 feet (12 m) wide. This was quite narrow, especially in comparison with its length. With only the 8-foot-deep (2.4 m) plate girders providing additional depth, the bridge's roadway section was also shallow.

The decision to use such shallow and narrow girders proved to be the original Tacoma Narrows Bridge's undoing. With such minimal girders, the deck of the bridge was insufficiently rigid and was easily moved about by winds; from the start, the bridge became infamous for its movement. A mild to moderate wind could cause alternate halves of the center span to visibly rise and fall several feet over four- to five-second intervals. This flexibility was experienced by the builders and workmen during construction, which led some of the workers to christen the bridge "Galloping Gertie". The nickname soon stuck, and even the public (when the toll-paid traffic started) felt these motions on the day that the bridge opened on July 1, 1940...

The wind-induced collapse occurred on November 7, 1940, at approximately 11:00 a.m. (PST), and was caused by a physical phenomenon known as aeroelastic flutter.

Leonard Coatsworth, a Tacoma News Tribune editor, was the last person to drive on the bridge:

Around me I could hear concrete cracking. I started back to the car to get the dog, but was thrown before I could reach it. The car itself began to slide from side to side on the roadway. I decided the bridge was breaking up and my only hope was to get back to shore. On hands and knees most of the time, I crawled 500 yards [1,500 ft; 460 m] or more to the towers… My breath was coming in gasps; my knees were raw and bleeding, my hands bruised and swollen from gripping the concrete curb… Towards the last, I risked rising to my feet and running a few yards at a time… Safely back at the toll plaza, I saw the bridge in its final collapse and saw my car plunge into the Narrows...

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