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Workers carry out maintenance on Chicago tower

14 August 2014 Last updated at 10:26 BST

Workers have been performing maintenance at the top of the John Hancock Center in Chicago.

The skyscraper is 1,127ft (344m) tall and is located in what is famously described as America's 'windy city'.

The tower was built in 1970 and has exactly 100 floors.

It has the fastest elevators in the US, which can travel from the lobby to the 96th floor observatory in 39 seconds.