Tacoma Narrows Bridge (1940)
The shallow and narrow girders are what caused the bridge to collapse.  With such small girders, the deck of the bridge was not rigid enough. It was easily moved by the winds. The bridge was well known for its movement. A small wind could make the center span move several feet during four- to five-second intervals. This was seen by the builders and workmen during construction. It caused some of the workers to name the bridge  "Galloping Gertie."  Even the public felt these motions on the day that the bridge opened on July 1, 1940.