As the first step in planning its new headquarters, Sears hired an interior design company, Environetics. Environetics designers studied how Sears’s office workers used their space every day. They learned how many workers each department had. They saw what equipment workers used. They watched how people traffic flowed through offices. They talked to Sears executives to learn how much the company planned to grow in the next ten or twenty years. Environetics told Sears that the company would need about 4 million square feet (371,612 sq. m). Half would be for present workers and half for the future. Sears executives realized that much space would mean a very tall building. In 1969 Sears hired the Chicago architectural firm of Skidmore, Owings & Merrill (SOM) to plan the tower.
Older office buildings had many inside walls, columns, and doorways. These held up the horizontal beams that formed floors and ceilings. But modern companies wanted floor plans with large open spaces and fewer dividing walls and columns. Removing interior walls and columns left architects with a problem. What would hold up each story’s ceiling? SOM’s chief engineer, Fazlur Khan, came up with one solution. Khan designed a system called bundled tubes. Skyscrapers could be built as a group of straight-