Tacoma Narrows Bridge

Tacoma Narrows Bridge

The Tacoma Narrows Bridge was the first suspension bridge across the Narrows of Puget Sound, connecting the Olympic Peninsula with the mainland of Washington, and a landmark failure in engineering history. Four months after its opening, on the morning of Nov. 7, 1940, in a wind of about 42 miles (68 km) per hour, the 2,800-foot (853-meter) main span went into a series of torsional oscillations the amplitude of which steadily increased until the convolutions tore several suspenders loose, and the span broke up. The bridge was designed to have acceptable horizontal displacement under the static pressure of a much larger wind, but was not designed to handle the dynamic instability caused by an interaction of the winds and the high degree of flexibility of the light, narrow, two-lane bridge. Modeling this type of fluid/structure interaction, a particularly simple type of flutter, was within the technical capability of engineers at the time, but was evidently not considered. A modern analysis would likely view the fluid/structure flutter as a bifurcation problem, and analyze the nature of the bifurcation as the wind speed increased. Immediately after the accident, numerous investigators were able to create both simple mathematical and scale physical models that exhibited the same failure as the actual bridge, and very simple models were able to predict the wind speed that would cause the collapse.