We've mentioned this one before - in Engineering's Ten Biggest Mistakes - but November 7th marks the anniversary of the collapse of Galloping Gertie, in Washington State.
"The original Tacoma Narrows Bridge, dubbed Galloping Gertie, was the world's third-longest suspension bridge when it opened on July 1, 1940. It collapsed in a windstorm about four months later, becoming famous as "the most dramatic failure in bridge engineering history."Note that no human life was lost during the bridge's closure. It has since been redesigned and rebuilt, as you can see on Wikipedia.
According to the website, "this footage is still shown to engineering, architecture, and physics students as a cautionary tale..."