2. 外语
  3. You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2 below. THE BRIDGE THAT SWAYED When th

You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2 below. THE BRIDGE THAT SWAYED When th

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问题 You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2 below.
THE BRIDGE THAT SWAYED
When the London Millennium footbridge was opened in June 2000, it swayed alarmingly. This generated huge public interest and the bridge became known as London’s "wobbly bridge."
The Millennium Bridge is the first new bridge across the river Thames in London since Tower Bridge opened in 1894, and it is the first ever designed for pedestrians only. The bridge links the City of London near St Raul’s Cathedral with the Tate Modem art gallery on Bankside.
The bridge opened initially on Saturday 10th June 2000. For the opening ceremony, a crowd of over 1,000 people had assembled on the south half of the bridge with a band in front. When they started to walk across with the band playing, there was immediately an unexpectedly pronounced lateral movement of the bridge deck. "It was a fine day and the bridge was on the route of a major charity walk," one of the pedestrians recounted what he saw that day. "At first, it was still. Then it began to sway sideways, just slightly. Then, almost from one moment to the next, when large groups of people were crossing, the wobble intensified. Everyone had to stop walking to retain balance and sometimes to hold onto the hand rails for support." Immediately it was decided to limit the number of people on the bridge, and the bridge was dubbed the ’wobbly’ bridge by the media who declared it another high-profile British Millennium Project failure. In order to fully investigate and resolve the issue the decision was taken to close the bridge on 12th June 2000.
Arup, the leading member of the committee in charge of the construction of the bridge, decided to tackle the issue head on. They immediately undertook a fast-track research project to seek the cause and the cure. The embarrassed engineers found the videotape that day which showed the center span swaying about 3 inches sideways every second and the south span 2 inches every 1.25 seconds. Because there was a significant wind blowing on the opening days(force 3-4)and the bridge had been decorated with large flags, the engineers first thought that winds might be exerting excessive force on the many large flags and banners, but it was rapidly concluded that wind buffeting had not contributed significantly to vibration of the bridge. But after measurements were made in university laboratories of the effects of people walking on swaying platforms and after large-scale experiments with crowds of pedestrians were conducted on the bridge itself, a new understanding and a new theory were developed.
The unexpected motion was the result of a natural human reaction to small lateral movements. It is well known that a suspension bridge has tendency to sway when troops march over
it in lockstep, which is why troops are required to break step when crossing such a bridge. "If we walk on a swaying surface we tend to compensate and stabilise ourselves by spreading our legs further apart-but this increases the lateral push". Pat Dallard, the engineer at Arup, says that you change the way you walk to match what the bridge is doing. It is an unconscious tendency for pedestrians to match their footsteps to the sway, thereby exacerbating it even more. "It’s rather like walking on a rolling ship deck-you move one way and then the other to compensate for the roll." The way people walk doesn’t have to match exactly the natural frequency of the bridge as in resonance-the interaction is more subtle. As the bridge moves, people adjust the way they walk in their own manner. The problem is that when there are enough people on the bridge the total sideways push can overcome the bridge’s ability to absorb it. The movement becomes excessive and continues to increase until people begin to have difficulty in walking-they may even have to hold on to the rails.
Professor Fujino Yozo of Tokyo University, who studied the earth-resistant Toda Bridge in Japan, believes the horizontal forces caused by walking, running or jumping could also in turn cause excessive dynamic vibration in the lateral direction in the bridge. He explains that as the structure began moving, pedestrians adjusted their gait to the same lateral rhythm as the bridge; the adjusted footsteps magnified the motion-just like when four people all stand up in small boat at the same time. As more pedestrians locked into the same rhythm, the increasing oscillation led to the dramatic swaying captured on film until people stopped walking altogether, because they could not even keep upright.
In order to design a method of reducing the movements, an immediate research program was launched by the bridge’s engineering designer Arup. It was decided that the force exerted by the pedestrians had to be quantified and related to the motion of the bridge. Although there are some descriptions of this phenomenon in existing literature, none of these actually quantifies the force. So there was no quantitative analytical way to design the bridge against this effect. The efforts to solve the problem quickly got supported by a number of universities and research organisations.
The tests at the University of Southampton involved a person walking on the spot on a small shake table. The tests at Imperial College involved persons walking along a specially built, 7.2m-long platform, which could be driven laterally at different frequencies and amplitudes. These tests have their own limitations. While the Imperial College test platform was too short that only seven or eight steps could be measured at one time, the "walking on the spot" test did not accurately replicate forward walking, although many footsteps could be observed using this method. Neither test could investigate any influence of other people in a crowd on the behavior of the individual tested.
The results of the laboratory tests provided information which enabled the initial design of a retrofit to be progressed. However, unless the usage of the bridge was to be greatly restricted, only two generic options to improve its performance were considered feasible. The first was to increase the stiffness of the bridge to move all its lateral natural frequencies out of the range that could be excited by the lateral footfall forces, and the second was to increase the damping of the bridge to reduce the resonant response.
Questions 14-17
Choose FOUR letters, A-I.
Write the correct letters in boxes 14-17 on your answer sheet.
Which FOUR of the following could be seen on the day when the bridge opened to the public?
A the bridge moved vertically
B the bridge swayed from side to side
C the bridge swayed violently throughout the opening ceremony
D it was hard to keep balance on the bridge
E pedestrians walked in synchronised steps
F pedestrians lengthened their footsteps
G a music band marched across the bridge
H the swaying rhythm varied to the portions of the bridge
I flags and banners kept still on the bridge
选项
答案B
解析 选项A“the bridge moved vertically”中的“moved vertically”是选项的关键内容，意思是上下垂直移动或晃动。而根据原文多处信息，例如第二段第三句话中的“lateralmovement”(侧向移动)和第六句话中的“sway sideways”(侧向摇摆)，可以看出伦敦千年桥并没有上下摆动，而是朝两侧左右摇摆，所以该选项为错误选项，应该排除。选项B“the bridge swayed from side to side”，根据前面一题的分析，该选项正确。选项C“the bridge swayed violently throughout the opening ceremony”，该选项的关键信息是“swayed violently”(猛烈摇摆)和“throughout the opening ceremony”(贯穿开幕仪式的始终)。而原文第二段中间现场目击者的描述明显提及“At first，itwas still．Then it began to sway sideways，just slightly”(一开始，桥梁并没有晃动，然后有轻微晃动)，再然后“when large groups of people were crossing，the wobbleintensified”(当人数变多时，晃动才加剧)。原文信息明显与该选项所说的“桥梁自始至终都在猛烈晃动”相反，所以该选项错误，应该排除。选项D“it was hard to keep balance on the bridge”，该选项内容在原文多处均有提及，例如原文第二段目击者的最后一句话“Everyone had to stop walking to retain balanceand sometimes to hold onto the hand rails for support”。所以该选项正确。选项E“pedestrians walked in synchronised steps”，该选项的关键在于“synchronisedsteps”(同步步伐)，原文第四、五段均有提及。第四段中间提及“It is an unconscious tendency for pedestrians to match theft footsteps to the sway,thereby exacer-bating it even more”，第五段最后提及“As more pedestrians locked into the samerhythm，the increasing oscillation led to the dramatic swaying captured on film…”，这里的“match their footsteps to the sway”和“locked into the same rhythm”对应选项中的“synchronised steps”。所以该选项正确。选项F“pedestrians lengthened their footsteps”，该选项的关键在于“lengthened theirfootsteps”(增大了他们的步伐)。而原文虽然在第四、五段提及关于行人步伐的理论，但是根本未提及行人是否“lengthened their footsteps”，所以该选项错误，应该排除。选项G“a music band marched across the bridge”，原文第二段开头虽然提及“band”，但是并未提及乐队是否也跟着过桥，只提到了人们伴随着乐队的演奏过桥(when they started to walk across with the band playing)，所以该选项不正确，应该排除。选项H“the swaying rhythm varied to the portions of the bridge”，该选项的关键在于“portionsof the bridge”(桥梁的不同部分)的摇摆节奏不同。该信息出现在原文第三段第三句话“…the center span swaying about 3 inches sideways every second and thesouth span 2 inches every 1．25 seconds”。这里明显能看出桥梁的中部与南部的摇摆节奏不同，与选项中的“varied to the portions of the bridge”对应，所以该选项正确。选项I“flags and banners kept still on the bridge”，原文第三段中间明显提及“there wasa significant wind blowing on the opening days．．．winds might be exerting excessiveforce on the many large flags and banners，but it Was rapidly concluded that wind buf-feting…”。原文这里提及虽然风力对桥上的旗帜和横幅有影响，但是并不足以使桥梁摆动。这也就是说桥上的“flags and banners”当天在风中是摆动的，而非静止的。所以该选项不正确，应该排除。综上所述，14-17题的正确答案为B、D、E、H。
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