The first Tacoma Narrows bridge was locally known as “Galloping Gertie,” since its slender design lacked stabilizing girders, causing it to twist and bounce in the wind. The bridge opened on July 1, 1940, after 29 months of construction and $18 million invested. On the first day of operations, 2,053 crossed the bridge after an inaugural parade of vehicles led by Gov. Clarence D. Martin and Tacoma Mayor Harry P. Cain. But Gertie’s life would be short-lived. A little over four months later, on Nov. 7 of the same year, the bridge collapsed during a massive windstorm. The high winds struck the Tacoma-Narrows Bridge at a critical angle and caused vibrations to set up, which eventually collapsed the bridge. Maximum wind speed, 31 mph in downtown Tacoma; probably higher over Puget Sound. The Tacoma Narrows Bridge, with a main span of 2,800 feet was the third-longest suspension bridge in the world at that time, Because planners expected fairly light traffic volumes, the bridge was designed with two lanes, and it was just 39 feet wide. This was quite narrow, especially in comparison with its length. With only the 8-foot-deep plate girders providing additional depth, the bridge's roadway section was also shallow. The decision to use such shallow and narrow girders proved to be the original Tacoma Narrows Bridge's undoing. With such minimal girders, the deck of the bridge was insufficiently rigid and was easily moved about by winds; from the start, the bridge became infamous for its movement. A mild to moderate wind could cause alternate halves of the center span to visibly rise and fall several feet over four- to five-second intervals. This flexibility was experienced by the builders and workmen during construction, which led some of the workers to christen the bridge "Galloping Gertie". The nickname soon stuck, and even the public felt these motions on the day that the bridge opened on July 1, 1940. The failure of the bridge occurred when a never-before-seen twisting mode occurred, from winds at 40 miles per hour. This is a so-called torsional vibration mode, whereby when the left side of the roadway went down, the right side would rise, and vice versa simply put the two halves of the bridge twisted in opposite directions, with the center line of the road remaining motionless. This vibration was caused by aeroelastic flutter. Fluttering is a physical phenomenon in which a structure becomes coupled in an unstable oscillation driven by the wind. Eventually, the amplitude of the motion produced by the fluttering increased beyond the strength of a vital part, in this case the suspender cables. As several cables failed, the weight of the deck transferred to the adjacent cables, which became overloaded and broke in turn until almost all of the central deck fell into the water below the span.
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