Tacoma Narrows Bridge disaster

Today is exactly 80 years since the famous bridge Tacoma Narrows collapsed, also known as "Galloping Gert". The bridge collapsed as a result of constructional defects and strong wind, which led to the bridge's deflection reaching 8.5 meters and 45 degrees.

Galloping Gerta

During a storm on November 7, 1940, the bridge reached an unusual oscillation, after which it spectacularly collapsed. Physicists spent a lot of time and energy over the years studying this event. Using analytical tools and digitalized footage of the disaster, physics students in both high school and college can continue this tradition.

This was the first bridge to use a series of tinsmiths as a roadway support. It was also the third largest hanging bridge at the time, with a central span of 853 meters and two side spans of 335 meters each.

On the day the Tacoma Narrows Bridge collapsed, a wind speed of about 19 m/s (70 km/h) blew. The center support vibrated torsionally at 36 cpm (cycles/min) in nine different segments. Over the next hour, the amplitude of torsional vibrations increased and movement changed from a rhythmic ascent and descent into a two-wave twist. In spite of all these movements, the middle part of the bridge remained stationary while the other two halves rotated in opposite directions.

The bridge was then noticeably twisted into two parts, experiencing 14 vibrations/min. This drastic torsional movement was initiated by damaging the tape joining the center of the diagonal strings. Due to the alternative deflection and collapse of the bays, the towers holding them were attracted to them. In addition, visible and dominant cracks developed before the entire bridge fell into the river.

The bridge fell about 11 o'clock in the morning, only four months after it was built.

Tacoma Narrows

Tacoma Narrows

Tacoma Narrows

07/11/2020     Wojciech Andruszkiewicz

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