【英语时差8，16】世贸大厦

 Amid the shocking events that occurred on September 11th, one of the most startling was the sight of the collapse¹ of the Twin Towers soon after hijacked² planes hit them. In this Moment of Science we explain how and why the collapse occurred. Designed and built in the 1960s, each tower had a tube structure, meaning that the concrete-encased steel columns that held the building up and bore its weight were on the building's exterior³. Inside, each Tower had a vertical⁴ steel core at its center that housed stairwells and elevators. Steel beams radiated outward from the core, supporting the floors and attaching to the exterior columns. Part of the reason that the buildings collapsed⁵ as they did is because aside from the floor reinforcements, there were no columns holding the building up from the inside.

When the planes hit they severely⁶ damaged the exterior columns. But the impact alone was not what caused the collapse; it was the intense heat generated by exploding airplane fuel. Each plane carried 24,000 gallons of fuel, enough to create fires hotter than 1472 degrees Fahrenheit⁷. Exposed to such intense heat, both the exterior columns and floor beams began to weaken. Consequently, the upper floors caved in, collapsing⁸ the floors below. The accumulated weight was enough to destroy the entire building.

Even though they eventually gave way, the Towers' structure saved thousands of lives by withstanding the heat for as long as they did, allowing many of the buildings' occupants to reach the ground. Had they been designed differently, the Towers might have fallen over like giant trees, creating a disaster of even larger proportions. 

1 collapse   

vi.累倒；昏倒；倒塌；塌陷

参考例句：

• The country's economy is on the verge of collapse.国家的经济已到了崩溃的边缘。
• The engineer made a complete diagnosis of the bridge's collapse.工程师对桥的倒塌做了一次彻底的调查分析。

2 hijacked   

劫持( hijack的过去式和过去分词 )； 绑架； 拦路抢劫； 操纵（会议等，以推销自己的意图）

参考例句：

• The plane was hijacked by two armed men on a flight from London to Rome. 飞机在从伦敦飞往罗马途中遭到两名持械男子劫持。
• The plane was hijacked soon after it took off. 那架飞机起飞后不久被劫持了。

3 exterior   

adj.外部的，外在的；表面的

参考例句：

• The seed has a hard exterior covering.这种子外壳很硬。
• We are painting the exterior wall of the house.我们正在给房子的外墙涂漆。

4 vertical   

adj.垂直的，顶点的，纵向的；n.垂直物，垂直的位置

参考例句：

• The northern side of the mountain is almost vertical.这座山的北坡几乎是垂直的。
• Vertical air motions are not measured by this system.垂直气流的运动不用这种系统来测量。

5 collapsed   

adj.倒塌的

参考例句：

• Jack collapsed in agony on the floor. 杰克十分痛苦地瘫倒在地板上。
• The roof collapsed under the weight of snow. 房顶在雪的重压下突然坍塌下来。

6 severely   

adv.严格地；严厉地；非常恶劣地

参考例句：

• He was severely criticized and removed from his post.他受到了严厉的批评并且被撤了职。
• He is severely put down for his careless work.他因工作上的粗心大意而受到了严厉的批评。

7 Fahrenheit   

n./adj.华氏温度；华氏温度计(的)

参考例句：

• He was asked for the boiling point of water in Fahrenheit.他被问到水的沸点是华氏多少度。
• The thermometer reads 80 degrees Fahrenheit.寒暑表指出华氏80度。

8 collapsing   

压扁[平]，毁坏，断裂

参考例句：

• Rescuers used props to stop the roof of the tunnel collapsing. 救援人员用支柱防止隧道顶塌陷。
• The rocks were folded by collapsing into the center of the trough. 岩石由于坍陷进入凹槽的中心而发生褶皱。