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Tacoma Narrows Bridge

The Tacoma Narrows Bridge is a pair of mile-long suspension bridges in the U.S. state of Washington, which carry State Route 16 across the Tacoma Narrows between Tacoma and the Kitsap Peninsula. They replaced a bridge that was opened to traffic on July 1 1940 and later became famous four months later for a dramatic wind-induced structural collapse that was caught on motion picture film. The original span's motion earned it the nickname "Galloping Gertie".

Due to materials shortages as a result of World War II, it took 10 years to build a replacement bridge, which opened October 14 1950. The 1950 replacement bridge was sometimes referred to as "Sturdy Gertie", and, like its predecessor, was the third longest suspension span in the world at the time of its construction. Population growth on the Kitsap peninsula caused the bridge to exceed its vehicle capacity, and a parallel bridge was constructed to carry eastbound traffic, while the 1950 bridge was reconfigured to carry westbound traffic. The new bridge opened July 15, 2007, making the Tacoma Narrows Bridge the longest twin suspension span in the world.

Galloping Gertie

The desire for the construction of this bridge dates back to 1889 with a Northern Pacific Railway proposal for a trestle, but concerted efforts began in the mid-1920s. In 1937, when the Washington State legislature created the Washington State Toll Bridge Authority and appropriated $5,000 to study the request by Tacoma and Pierce County for a bridge over the Narrows.

The first Tacoma Narrows Bridge opened to traffic on July 1 1940. It collapsed four months later on November 7 1940, at 11:00 AM (Pacific time) due to a physical phenomenon known as aeroelastic flutter caused by a wind. The bridge collapse had lasting effects on science and engineering. In many undergraduate physics texts the event is presented as an example of elementary forced resonance with the wind providing an external periodic frequency that matched the natural structural frequency (even though its real cause of failure was aeroelastic flutter). Its failure also boosted research in the field of bridge aerodynamics/aeroelastics which have themselves influenced the designs of all the world's great long-span bridges built since 1940.

No human life was lost in the collapse of the bridge. The collapse of the bridge was recorded on film by Barney Elliott, owner of a local camera shop, and shows Leonard Coatsworth leaving the bridge after exiting his car. In 1998, The Tacoma Narrows Bridge Collapse was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant." This footage is still shown to engineering, architecture, and physics students as a cautionary tale.

After the collapse, two bridges were constructed in the same general location. The first one, now called the Tacoma Westbound bridge, is 5,979 feet (1822 m) long — 40 feet (12 m) longer than Galloping Gertie. The second one, the Tacoma Eastbound Bridge, opened in 2007.

Westbound bridge

The current westbound bridge was designed and rebuilt with open trusses, stiffening struts and openings in the roadway to let wind through. It opened on October 14 1950, and is 5,979 feet (1822 m) long — 40 feet (12 m) longer than the first bridge, Galloping Gertie. Local residents nicknamed the new bridge Sturdy Gertie, as the oscillations that plagued the previous design had been eliminated. This bridge along with its new parallel eastbound bridge are currently the fifth-longest suspension bridges in the United States.

When built, the westbound bridge was the third-longest suspension bridge span in the world. Like other modern suspension bridges, the westbound bridge was built with steel plates that feature sharp entry edges rather than the flat plate sides used in the original Tacoma Narrows Bridge (see the suspension bridge article for an example).

The bridge was designed to handle 60,000 vehicles a day. It carried both westbound and eastbound traffic until the eastbound bridge opened on July 15, 2007.

Eastbound bridge

In 1998, voters in several Washington counties approved an advisory measure to create a second Narrows span. Construction of the new span, which carries eastbound traffic parallel to the current bridge, began on October 4 2002, and was completed in July 2007. The Washington State Department of Transportation collects a toll before entering the eastbound span, at $2.75 for Good to Go! account holders with in-vehicle transponders and a $4.00 toll for cash/credit card paying customers. The existing span has been toll-free since 1965. The new bridge marks the first installation of the new Good To Go! electronic toll collection system.

A group called NarrowsBridgeLights.org advocates illuminating both bridges with twinkling lights. The group recommends solar powered lighting, for both safety and beauty.

Gallery

References

External links

Historical

Second span project

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