The failure of the Tacoma Narrows Bridge

The original design of the Tacoma Narrows Bridge developed by Washington State engineer Clark Eldridge included a suspension bridge with a center span of 2,600 feet (792 m), two side spans of 1,300 feet (396 m) each, trusses and cables 39 feet (11.9 m) center to center, stiffening trusses 22 feet (6.7 m) deep, and two travel lanes and sidewalks. However, when the Washington State Toll Bridge Authority (WSTBA) requested federal assistance from the Public Works Administration (PWA), the PWA agreed to a grant of 45% of the construction cost on the condition that the WSTBA hire Leon Moisseiff of New York for the design of the superstructure. Moisseiff told the PWA that his design would reduce estimated construction cost from $11 million to $7 million. The foundation design was to be performed by another New York firm, Moran, Proctor, and Freeman. Moisseiff increased the center span length to 2,800 feet (853.4 m) and reduced the side span lengths to 1,100 feet (335.3 m). The 25-foot deep (7.6 m) stiffening trusses were replaced by 8-foot-deep plate girders. On July 1, 1940, the bridge was opened to traffic. It was the third longest bridge in the world after the Golden Gate and George Washington Bridges. On November 7, 1940, torsional oscillations caused the failure of the bridge. The wind speed was about 42 miles per hour. Due to World War II, construction of the new bridge was delayed, and it was finally opened in 1950 with one twist: the new bridge had stiffening trusses 33 feet (10 m) deep or more than four times the depth of the plate girders designed by Moisseiff. This paper covers the construction and destruction of the original bridge and the people connected to it.