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The original Tacoma Narrows Bridge, connecting Tacoma and Gig Harbor, opened to the public on July 1, 1940. A little more than four months later on November 7, a moderate windstorm (40 MPH) caused the 5,939 foot-long bridge to meet a spectacular demise when parts of it crashed into Puget Sound.

When the bridge opened in July, the public immediately gave her the name "Galloping Gertie" due to the way she would "gallop" in relatively light winds. In fact, many drivers saw and felt the wave motion of the bridge as cars in front would disappear momentarily and driving across the bridge had a feeling of a roller coaster ride. Obviously this is extremely bad for a bridge to do and attempts were made to rectify the situation but none worked out. If that wasn't enough, the bridge was designed to catch the wind instead of letting it flow through, thus increasing the rolling motion of the bridge and as was the trend at the time, the bridge was built with maximum lightness, slenderness, and flexiblity.

Finally, on the day of its collapse, the bridge started a corkscrew motion that continued to increase until the bridge's main span had a 600 foot-long chunk break off, turn upside-down and crash into the Narrows (The part of Puget Sound that separated the peninsula and the Washington mainland). At its peak the difference in height between the two sides of the bridge reached 28 feet, and afterwards the other two spans sagged 45 feet along, also causing the main towers to buckle under the increased weight.

Today, most people accept that the bridge's demise was caused by resonance, however some believe it may have been caused by self-excitation. In 1992 the underwater remains of the bridge were put on the National Register of Historical Places to prevent salvagers from taking pieces of it. Also, a new Tacoma Narrows Bridge was built 10 years later, and after 29 months of construction was opened on October 14, 1950.


http://www.ketchum.org/tacomacollapse.html
http://www.nwrain.com/~newtsuit/recoveries/narrows/narrows.htm