Collapse of Tacoma Narrows Bridge


Tacoma Narrows Bridge was a suspension bridge that was built in 1940, in Tacoma city, which is in the state of Washington, and it was the third-longest suspension bridge at the time of its construction. Also, natives of the city gave the nickname of “Galloping Gertie” to the bridge, because of the vertical movements it made. The bridge was opened to the public, after 2-years long construction process, on July 1, 1940 and after 4 months, it collapsed under 64 km/h wind-based resonance.

It was designed by one of the famous engineers of that time: Leon Moisseiff, who served in the construction of Golden Gate Bridge which has a bad reputation with suicides. The bridge was 1810,2 meters long and 853,4 meters wide and going to be one of the biggest projects of that time. Yet, the vertical movements of the bridge were realized at the beginning of the construction process and as a result of this problem, Moisseiff was contacted swiftly and got information about the issue. He admitted that the same movements with much fever sizes are seen on the last 2 bridges he designed (Deer Island Bridge, Bronx-Whitestone Bridge).

For the equilibration of the bridge’s vertical movements, workers immediately started to work. While the construction of the bridge was proceeding, to serve as an anchor, temporary connecting-cables, which are dangling from the sides of the bridge, were used and upon the ceasing of the movement, it was believed that the problem was solved with this solution.

However, the incident which revealed that the solution had been faulty, started on November 1, with the harsh winds’ breaking off the cables of the bridge. On November 7, 1940, from 08:30 AM, the bridge’s vertical movements started to increase visibly. The bridge was swinging as if it was a plastic, and it was not only terrific but also exciting scene for the viewers. Suddenly, at 10:03 AM, the bridge started to make lateral movements and those movements reached to terrible sizes in a short time. The bridge was moving in a way that 45 degrees and approximately 8.5 meters long height difference between two ends. Eventually, bridge’s natural frequency and the gradually increasing movements’ frequency collision made the bridge collapse. Just before the collapse, the bridge was pedestrianized, so the only casualty in the disaster was the death of a dog which was left in a car. The collapse of the bridge stunned the country and the world. In a consequence of a disaster like that, designs of the suspension bridges were modified on a large scale and it has a great deal of contribution on the study of these kinds of disasters’ prevention techniques.


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