Most people have seen the film of ‘Galloping Gertie’, the Tacoma Narrows bridge collapsing. This was caused by the lack of stabilizing trusses. The Golden Gate bridge and the George Washington bridge were also built this way. Both bridges have since had a retrofit to add the needed support. Before the retrofit the Golden Gate bridge had also been experiencing some unexpectedly large fluctuations even in moderate winds.

(The Great Courses – Understanding the World’s Greatest Structures)