Tacoma Narrows Bridge

The Tacoma Narrows is the only point in the Puget Sound where the Washington mainland and the Olympic Peninsula come close together. It was very clear that a bridge was needed to cross over the Narrows and join the peninsula. With this in mind, the state of Washington created the Washington Toll Bridge Authority in 1937, with full intentions of financing, constructing, and operating a toll bridge. From this authority, the Tacoma Narrows Bridge underwent construction.

The Tacoma Narrows Bridge was to be completely revolutionary in its design. It was to be a suspension bridge that was structurally light, graceful, and flexible. With all these characteristics in mind, what was created was a very artistic bridge. Its artistic design later demonstrated an aerodynamic phenomenon that brought the bridge to its end after approximately four months.

Construction on the bridge was finished in July of 1940. The bridge cost approximately $7 million dollars and took over two years to complete. Its length was 5,939 feet, and its design worked around eight foot girders. These girders allowed to flexibility. The bridge was open for two lanes of traffic, and included two sidewalks.

Once opened, the locals lost no time in nicknaming the bridge "Galloping Gertie." Breezes as low as 4mph caused the roadbed and bridge to oscillate vertically. Fascination with the bridge spread rapidly. Thousands of people drove from across the country to experience crossing the swaying bridge. When crossing the bridge,cars would disappear and reappear with the oscillations. Many concerns had been voiced about the bridges stability, but officials were so confident of its design that they actually considered canceling the insurance policies on the bridge.

The popularity of the bridge continued for four months. The bridge authority thrived as traffic exceeded far more than what had ever been expected. Then rolled along November 7, 1940. Early in the morning the bridges center span had been rising and falling up to 5 feet due to winds of 35 to 46 miles per hour. This constant motion alarmed officials and caused them to close the bridge at 10am. Eventually, the rising and falling turned into a twisting motion, which grew stronger with each twist. These movements went rapidly from 5 feet to 28 feet, tilting the roadbed at 45ƒ from side to side. The center of the bridge endured about 30 minutes of the twisting motion. At about 10:30am, the center span floor panel dropped into the water far below. The roadbed was breaking up and chunks of concrete were falling into the water. At 11:02am, 600 feet of the western end of the bridge twisted free, flipped over, and fell into the water. The twisting motion continued on the remaining parts of the bridge sections, and at 11:09am they also plunged down into the water. All that was left of the bridge were the side spans that sagged 30 feet.

The collapse of "Galloping Gertie" served a very good purpose. It brought to all engineers' attention that new research was necessary to understand what had happened. Resonance and the aerodynamic shape of the bridge were the main problems with the design of the bridge. The shape of the bridge acted as an airplane wing, and the wind passing under the bridge acted as lift for the bridge, which explains the vertical oscillations. Resonance is the motion of some action due to an external force. The external force in this case, being the wind. From the start it was obvious that the bridge was not very stable, however, much was learned from its failure. The remains of the disaster were recovered and placed in the Nation Register of Historic Places. In 1950, a more safe and new Tacoma Narrows Bridge was built.

Movie of the Tacoma Narrows Bridge- shows the bridge twisting

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