KXJB-TV mast situated at Galesburg, North Dakota is with a height of 628 metres the second tallest construction in the world (and the third tallest ever built). KXJB-TV mast was first built in 1966. Since then, it collapsed twice!
First on February 14th, 1968 after a helicopter collision and then on April 6th, 1997, because of icing.

http://upload.wikimedia.org/wikipedia/en/thumb/b/be/453px-KXJBfrombase.jpeg
KXJB-TV mast

More information about this giant, which collapsed twice on
http://en.wikipedia.org/wiki/KXJB_Tower
http://www.structurae.net/structures/data/index.cfm?ID=s0014122
http://www.structurae.net/structures/data/index.cfm?ID=s0014123
http://www.structurae.net/structures/data/index.cfm?ID=s0014124
http://web.archive.org/web/20001212211400/http%3a//www.kx4.com/kxjb_tower.html
http://wireless2.fcc.gov/UlsApp/AsrSearch/asrRegistration.jsp?regKey=602919
http://www.skyscraperpage.com/cities/?buildingID=1322
http://www.skyscraperpage.com/diagrams/?b1322

Omg.