Question

Exercise#7 In your opinion how did the world trade center collapse, change and redefine the culture and construction of today 1-Identify and name three ways we changed the built environment due to the 9/11 events 2-Analyze if these are functioning well or net and why?

Answer 1

Answers:

Ans 1 = In the 9/11 attack on the World Trade Center, the steel columns got exposed to high temperatures due to the burning of fuel from the airplane.While a number of columns got destroyed by the impact itself. the rest collapsed under the immense heat produced.this sort of collapse is not ordinary as steel melts at 1200 - 1500 C. It is a progressive collapse and it can be controlled by modification in design in the following ways:

1. providing High ductility

this prevents the reinforcement from breaking suddenly and becoming more heat resistant. This has also resulted in increased protection against earthquakes.

2. Increasing redundancy of the structure to avoid progressive failure.

3. the concrete strength can be increased and for such commercial buildings safeguards can be upgraded to assimilate this high concrete quality standards.

4. the reinforcement itself can be improved and made blast resistant.

Ans 2-

1. The American Codes are well equipped to provide for the extra ductility in the structural supports. In important structures , they are designed to survive an earthquake with a return period of 2000 years. But blast resistance is effectively taken into account. As it is still a developing issue and research is conducted, it can be improved in near future.

2.The compressive strength of concrete used in World trade center was around 12000 psi. This material density can be increased and the resulting strength is as much as 30000 psi which is sufficient to be called fireproof even after blasts which causes high pressure and stress in the concrete.

3.Steel microfibres are mixed with the concrete itself apart from reinforcement. this increases the bond strength between concrete and steel and makes the formation tough and blast resistant. the cracks an also be prevented from spreading.