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Fall of the twin towers
First published September 12, 2001

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The twin towers were built between 1966 and 1973 to the design of Minoru Yamasaki (deceased). To gain an elegant form to house the huge rentable area required, he chose to have two tall slender towers.

To make this structurally viable, Skilling, Helle, Christiansen, Robertson Structural Engineers gave the towers an external steel lattice that acted as a wind brace. This system was first used at the IBM building in Seattle. This system also eradicated the need for internal columns - these would have been next to impossible on buildings of this size due to the required size of the columns in the lower part of the structure. The lattice was shaped to appear as oversized window mullions, spaced at 39 inches. They really were huge, but felt reassuring for anyone with a sense of vertigo.

This was also the first building to employ the skylobby system - this is a highly efficient way of working the lifts to service the huge building population. Express lifts would take people to "skylobbies" from where there could ascend to their own "local level". This cut the number of lifts down, again increasing leasable are per floor to a percentage more like that of a conventional lowrise building.

In 1993, a massive bomb exploded in the World trade Center's underground carpark, killing six people and injuring 1042. The bomb failed to budge the buildings due to the exoskeletal structural system, which had little reliance on the foundations of the core.

On September 11, 2001, the twin towers and tower 7 were reduced to rubble after terrorists hijacked two american Boeing 767s and flew them into the towers. The tragedy still unfolds. Minoru Yamasaki Architects have this to say:

"MYA is shocked and outraged at this terrible tragedy. Mere words cannot express the depth of our grief and our thoughts and prayers go out to the victims and there families."

statistics:
floor area: 40,000 sq. feet in each of the upper floors.Total 9,6000,000 square feet gross.
height: 110 floors, rising 412metres.
elevators: 99.
population: 50,000, plus 70,000 daily visitors.
tallest tower: until 1974 when Sears Tower overtook them.

by Peter Johns
[DCM employee during sketch design of the Grollo Tower, which employed similar systems.]
[visitor to WTC, 1989]

related:



<<Down went not simply the leading architectural icon of global capital but the most concentrated symbol of human density - of the coming together that has, in one form or another, guided urbanism from its beginnings.>>
MICHAEL SORKIN IN METROPOLIS MAGAZINE JANUARY 2002

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