World Trade Center

To work on Yamasaki’s design the structural firm Worthington, Skilling, Helle & Jackson worked to develop the tube – frame structural system used in the Twin Towers. The World Trade Center towers utilized high – strength, load bearing perimeter steel columns that were spaced closely together to form a strong, rigid structure to support all lateral loads such as wind loads and sharing the gravity load with the core columns. The structure containing 59 columns per side was constructed with extensive usage of pre – fabricated modular pieces each consisting of three columns, three stories tall and connected by plates. The plates were welded to the columns to create the off – site modular pieces, at the fabrication shop.
The core of the towers contained the elevator and shafts, the restrooms, three stairwells and other support spaces. The core was made of steel and concrete mixture to make it strong enough to bear any stress and the core of each tower was a rectangular area that is 87 by 135 feet and contained 47 steel columns running from the bedrock t the top. The floors supported their own weight and the human’s load also providing lateral stability to the exterior walls and distributing the wind loads among the exterior walls.
The trusses located from the 107th floor were designed to support the tall communication antenna on the top of the North tower that was fixed in 1978. The tube frame design using steel and concrete at a time and also sprayed by the fire resisting material.
But despite these measures and such a strong structure the Twin Towers could not stand the crash of the planes and were grounded on September 9, 11. May be there were some flaws left in the structure.