From one of the captions of the photos at this site:
The Skyscraper Museum: VIVA2
"The height of the towers was generally described as 110 stories, but from the perspective of design and construction, the structures rose more than 1,430 feet above their foundations in bedrock. They were among the first of the new type of skyscraper to use "tube" construction in which the outside walls of structural steel acted as a thin shell, carrying the buildingÂ’s weight. The tube cantilevered from its foundations to supply all of the resistance to wind and earthquake forces and to stabilize the core against lateral buckling. This "open plan" office was a favored feature of postwar office buildings and contrasted dramatically with the typical space in earlier twentieth-century skyscrapers such as the Empire State, where a 3D grid of the steel skeleton structure placed columns every 18 to 22 feet. The system eliminated the need for a conventional rigid skeleton frame and allowed for a reduced story height of 12 feet and floors with a column-free, clear span of up to 60 feet.
Both towers were 209 feet square, with chamfered corners to aid in construction. The 59 columns per side were closely spaced, with 22 inches of window and an 18-inch column, a total of 40 inches per bay. The floor plans of the Twin Towers comprised an acre, minus the core area of elevator shafts, circulation, and mechanical systems. "