Dome

Close view of the southwest corner, depicting mechanical floor; The Sears Tower is a skyscraper in Chicago, Illinois. It has been the tallest building in the United States since 1973, surpassing the World Trade Center, which itself had surpassed the Empire State Building only a year earlier. Commissioned by Sears, Roebuck and Company, it was designed by chief architect Bruce Graham and structural engineer Fazlur Khan of Skidmore, Owings and Merrill. Black bands appear on the tower around the 29th-32nd, 64th-65th, 88th-89th, and 104th-109th floors. These are louvers which allow ventilation for service equipment and obscure the structure's belt trusses which Sears Roebuck did not want to be visible as on the John Hancock Center. Source: Wikipedia; http://en.wikipedia.org/wiki/Main_Page (accessed 11/4/2007)