阅读理解
The opinion of many engineers is that the architects that designed the New York World Trade Center
Twin Towers did a good job in designing the buildings. The buildings were safe from the hazards
envisioned (预想到的) at the time. Indeed, they were designed to withstand the force of aircraft that might crash into them. They were not however, designed to withstand the effects of the very high temperatures
produced by the ignition (点燃) of aviation fuel carried by the aircraft.
Steel lightly covered with concrete is the main structural part of the towers and steel loses a lot of
structural strength when heated to 1100 degrees Centigrade and beyond, as it was. To protect the steel the towers beams were coated with a few centimeters of concrete. That insulation (隔离) was to provide
structural state of being complete for at least 1 hour of fire. The towers met that test. The south tower
lasted 62minutes. The north, 103 minutes. Tragedy followed when not all could escape before the
collapse.
Most experts agree that the Twin Towers were very well designed. Many also agree that the people
planning the attacks were very knowledgeable and aimed the aircraft at a height that would produce the
most damage. The aircraft crash and the resulting fuel fed fires were aimed at about the 90th floor. That
was just high enough to insure that the upper floors would weaken with the heat and crack down, dropping into the remaining part of the building.
The mass of the falling top floors created such a falling load that some experts estimate it exceeded by 5 to 10 times normal bearing loads. The effect was like a giant hammer, each floor contributing more weight
to be born by the next floor down.
Were the Trade Towers well designed? Engineers say yes. But, the public holds to the belief that
architects will never again design a tall building without considering the effects of terrorist attacks of all
potential kinds. That not only includes the ability of the structure to withstand attack but the means to allow the buildings occupants to escape in time to survive.
1. Many engineers believe that the Twin Tower was well-designed after September 11 because _________________.
A. it could withstand aircraft crashing into it at the moment
B. it could withstand any natural hazards such as earthquake or fire
C. it had an attracting and beautiful appearance until they were destroyed
D. they had the miserable honor of being selected as the target of terrorist attack
2. According to the article, those who designed the tower could have done better if _______.
A. the tower lasted longer after being attacked
B. the tower held stable until all of the people in there managed to escape
C. the tower can be immune to such attacks
D. they considered more about the effects of the very high temperatures and made duel(决定性的)
changes in the structure
3. The part of the building below 90th floor _____________.
A. remained where they were
B. cracked down because of the burning
C. was hammered down by the falling upper part
D. was safe after the attack
4. The author believed that the Twin Towers ____________.
A. were not well- designed
B. were well-designed
C. were good examples for engineers of our time
D. were out of consideration when we talk about engineering later
