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Sears Tower


    This 110-storey skyscraper in Chicago, USA, is the tallest building in the world. Sears Tower is 443 meters high, which is over 50 meters taller than the Empire State Building in New York City. The tower was originally built as the national headquarters of the Sears, Roebuck Company.

THE BEGINNING
    People generally agree that the skyscraper was invented in Chicago, the third largest city in the USA. In 1871 a fire destroyed a third of the city, and architects set about rebuilding it. By this time, steel was being mass produced and in 1852, Elisha Otis had invented the lift. New buildings could safely and practically be made much taller. The first high-rise building appeared in the city in 1882. This was the Home Insurance Company Building. It was the first building to have a skeleton structure made entirely of steel and iron. It had ten floors – a hundred fewer than Sears Tower, built 90 years later.

BUILDING UPWARDS
    As the demand for land in city centres grew, people needed to build fast and economically. Skyscrapers were the perfect solution. With new materials and technology, the design of skyscrapers was gradually improved and perfected. Steel girders were used in different ways to make a strong framework. Some buildings were made of tall steel tubes designed to withstand the winds that blow around the top levels. Inside the tubes; individual floors and rooms are rigid so that people can live and work safely and comfortably.



THE ULTIMATE SKYSCRAPER
    It took 2400 workers three years to build Sears Tower, which was finished in 1973. The tower's unique framework is made up of nine square tubes, which form a large square at the base. This rests on concrete, rock-filled shafts that are securely fitted into the solid rock beneath. The nine welded steel tubes rise 50 floors up. Then the building starts to narrow. Seven tubes continue on up to the 66th floor. Then five rise on to the 90th floor, leaving just two tubes to form the top 20 floors. Two television antennae take the building's total height to 520 meters - over half a kilometer. The amount of steel used to build the framework was enough to make more than 52,000 cars.

OPERATING THE BUILDING
    This huge building has over 418,000 square meters of space. That's more than 57 football pitches. The Tower has 104 high-speed lifts, which divide the building into three separate zones and make it easier for people to find their way around. The fireproofed frame is covered in a skin made of black aluminium and more than 16,000 bronze-tinted glass windows. Six automatic window-washing machines clean the whole of the building eight times a year.

TOURIST ATTRACTION

About 1.5 million tourists visit Sears Tower each year. Two express lifts take them up to the 103rd floor in just over a minute. From the tower's Skydeck, visitors have spectacular, panoramic views of Chicago. In the building's lobby there is an enormous 'wall mobile' by the famous sculptor Alexander Calder.



























































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