A strom rolled in with high winds during the Bluesfest concert causing the main stage to collapse. Cheap Trick was performing a left the stage minutes before the collapse due to the storm:
http://www.obj.ca/Local/Sports-and-entertainment/2011-07-17/article-2658137/BREAKING:-Main-stage-collapses-at-Bluesfest/1
Dramatic video shows a stage collapse in Ottawa at the Bluesfest
http://www.obj.ca/Local/Sports-and-entertainment/2011-07-17/article-2658137/BREAKING:-Main-stage-collapses-at-Bluesfest/1
Dramatic video shows a stage collapse in Ottawa at the Bluesfest