WILLIS TOWER, CHICAGO
The Sears Tower, now known as Willis Tower, was the tallest building in the world when it was completed in 1973, a position it would hold for the next 25 years. It is still the tallest building in North America. It originally was constructed to consolidate all merchandising offices of the Sears & Roebuck Co. into one building. This was accomplished in the first fifty floors, each of which covers 50,000 square feet. The design of the building was decided on over lunch at the Chicago Club. Engineer Fazlur Khan believed that the bundled tube system would be the most efficient for a building of such magnitude, but he worried about the aesthetics. Architect Bruce Graham, however, used a handful of cigarettes to illustrate how each tube could rise to a different height. In 2009, a retractable glass balcony was added to the 103th floor Skydeck, which continues to keep the observatory as one of Chicago’s top architectural attractions. theskydeck.com