Origonal Tacoma Narrows Bridge
The first Tacoma Narrows bridge (not to be confused with the rebuilt bridges that came after it) was opened on July 1, 1940. It was a grand suspension bridge, with a span of almost six thousand feet. It cost six million dollars to build. However, it lasted only a little more than four months.
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The bridge had problems with rippling from the beginning. Nicknamed "Galloping Gertie", the suspension bridge often bounced and swayed with the wind. During construction, workers on the bridge chewed lemons to combat seasickness. The bridge had been designed to be flexible, but something still seemed off. Engineers at the time were not fully aware of aerodynamic forces, so they were not fully accounted for in the design. Engineering Professor F. Bert Farquharson at the University of Washington was put in charge of studies, to see how to better the bridge. He conducted wind tunnel studies with his group of students. They found the same force that later destroyed the bridge in their models.
The morning that the Tacoma Narrows bridge collapsed, plans were being made to make the bridge more streamlined, so that the wind would have less area to push against, lessening the bridge's movements. These plans could be carried out within forty-five days. There would not be time for that, however. On November 7, 1940, the bridge collapsed.
That morning, the wind was blowing at thirty-five to forty miles per hour. The bridge had been built to withstand winds up to one hundred twenty miles per hour, and had been in winds of fifty miles per hour with no problems during the fall. That day, however, the wind was directly hitting the solid metal plates on the sides of the bridge. The bridge began to twist. It took four minutes for the twisting to go from small movements to huge ones. For a while, the bridge would twist so that one edge was twenty-eight feet above another. The bridge twisted at forty-five degree angles. For an explanation on how relatively small winds could cause this, go to the "Forces Acting on Bridges" tab, and then the "Resonance" tab.
The morning that the Tacoma Narrows bridge collapsed, plans were being made to make the bridge more streamlined, so that the wind would have less area to push against, lessening the bridge's movements. These plans could be carried out within forty-five days. There would not be time for that, however. On November 7, 1940, the bridge collapsed.
That morning, the wind was blowing at thirty-five to forty miles per hour. The bridge had been built to withstand winds up to one hundred twenty miles per hour, and had been in winds of fifty miles per hour with no problems during the fall. That day, however, the wind was directly hitting the solid metal plates on the sides of the bridge. The bridge began to twist. It took four minutes for the twisting to go from small movements to huge ones. For a while, the bridge would twist so that one edge was twenty-eight feet above another. The bridge twisted at forty-five degree angles. For an explanation on how relatively small winds could cause this, go to the "Forces Acting on Bridges" tab, and then the "Resonance" tab.
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In an hour, a six hundred foot long chunk of the bridge deck fell off. Within eight minutes of the first piece, the entire bridge fell. The only death was a dog inside a car stalled on the bridge. The dog was too frightened for an attempt at its rescue to be successful. To see a video of the collapse, go to the link below:
While the Tacoma Narrows bridge was destroyed, a lot was learned from its failure. Engineers learned that wind should be allowed to pass through the sides of bridges, and that there should be limited surface area on a bridge facing directly towards the wind. Also, the importance of testing bridge designs with wind tunnels before construction was shown. And finally, if a bridge is found faulty in experiments with models, closing the bridge should be considered.