Materials and structures

The collapse of the World-Trade Center towers, on September 11, 2001, has raised questions about the design principles in high-rise buildings. In this article, we first consider the likely failure mechanisms that may have ultimately led to the collapse of the Twin towers. This analysis is based on a materials -to-structures approach, in which we look both at the characteristic behavior of the construction materials and the design details of the buildings. The very fact that the buildings survived the crash of the planes into the buildings suggests that a time dependent behavior at the material level affected the structural stability of the structure to the point of failure. On the other hand, the failure per se reveals the existence of a weakest link in the structural system, which ultimately failed because of a lack of redundancy. We then turn to the question whether ─from an engineering point of view─ skyscrapers will continue to have a future in the 21 st century despite the increased vulnerability of our mega-cities. New materials -to-structures engineering solutions are also discussed, which in time could provide a new technology of redundancy to ameliorate the vulnerability of critical engineering structures.