At the time of the creation, the structural arrangements of the buildings were truly revolutionary. Firstly, the architects have used for the construction of skyscrapers, a new system with bearing beams and columns, which are separated by a space. However, engineers have proposed a radically new view of the structure of the building – it was called the principle of pipe-frame. With this innovation the twin towers were robust and resistant not only to the side and wind loads, but also to gravity.
Building a shopping center for the first time faced with serious problems in February 1975, when a fire started on the eleventh floor of the north tower of the World Trade Center. The fire spread through the central tube up to 9 and 14 floors (Glans and Lipton 34). The investigation revealed the fact that the fire happened in the office on the 11th floor, and the reason was negligence. In 1993 there was the first terrorist attack of the World Trade Center, which killed 6 people and injured more than 1,000. The explosion took place in the North Tower of the World Trade Center, when a truck drove into the underground garage with 680 kg of explosives in it.
First terrorist attack
