THE BRIDGE THAT SWAYED - IELTS Reading Answers & Explanations
From IELTS Recent Actual Test 3 Academic Reading Test 1 · Part 2 · Questions 14–26
Reading Passage
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 Paul's Cathedral with the Tate Modern 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
Questions 14–17 Multiple Choice (Four Answers)
Choose FOUR letters, A-I.
Write the correct letters.
Questions 18–23 Summary Completion
Complete the summary below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
To understand why the Millennium Bridge swayed, engineers of Arup studied the videotape taken on the day of the opening ceremony. In the beginning they thought the forces of 18 might have caused the movement because there were many flags and banners on the bridge that day. But quickly new understandings arose after series of tests were conducted on how people walk on 19 floors. The tests showed people would place their legs 20 to keep balance when the floor is shaking. Pat Dallard even believes pedestrians may unknowingly adjust their 21 to match the sway of the bridge. Professor Fujino Yozo's study found that the vibration of a bridge could be caused by the 22 of people walking, running and jumping on it because the lateral rhythm of the sway could make pedestrians adjust their walk and reach the same step until it is impossible to stand 23.
Questions 24–26 Table Completion
Complete the table below.
Choose NO MORE THAN THREE WORDS from the passage for each answer.
| Test conducted by | Problems of the test |
|---|---|
| 24 | Not enough data collection |
| 25 | Not long enough |
| 26 | Not like the real walking experience |
Answers & Explanations Summary
| # | Answer | Evidence | Explanation |
|---|---|---|---|
| Q14 | — | — | |
| Q15 | — | — | |
| Q16 | — | — | |
| Q17 | B / D / E / H | 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 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 As more pedestrians locked into the same rhythm, the increasing oscillation led to the dramatic swaying captured on film |
Excerpt/Passage Explanation: The passage says that the bridge started moving from side to side, and the movement became so strong that people had to stop walking and hold on to keep from falling. It also explains that a video showed the middle part of the bridge and the south part were moving at different speeds. Finally, it notes that the swaying got much worse because many people started walking with the same rhythm as the bridge's movement. Answer Explanation: The answer is that on the day the bridge opened, it moved from side to side, people had trouble keeping their balance, people's steps became synchronized with the movement, and different parts of the bridge swayed at different speeds. Reason For Correctness: The correct answer identifies four observations from the opening day described in the passage. First, the passage states the bridge had a "pronounced lateral movement" and began to "sway sideways," which means it moved from side to side (B). Second, a person who was there said, "Everyone had to stop walking to retain balance," showing it was hard to keep balance (D). Third, the explanation for the swaying was that pedestrians unconsciously "match their footsteps to the sway," meaning they walked in synchronized steps (E). Finally, video from that day showed that different parts of the bridge moved differently: the "center span" and the "south span" swayed at different speeds and distances, so the rhythm varied (H). |
| Q18 | wind / winds | the engineers first thought that winds might be exerting excessive force on the many large flags and banners | Excerpt/Passage Explanation: The passage says that at the start, the engineers' first idea was that the wind was creating a very strong push ('excessive force') on the big flags and banners on the bridge. Answer Explanation: The answer means the moving air outside. Reason For Correctness: The correct answer is 'wind' or 'winds'. The summary asks what engineers first thought caused the bridge to move. The passage says that at the beginning ('first thought'), engineers believed that 'winds' were pushing on the flags and banners, which made the bridge sway. |
| Q19 | swaying | 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 | Excerpt/Passage Explanation: The passage says that scientists got new ideas after they did tests. These tests included watching how people walked on platforms that were moving from side to side. They also did large tests with many people on the actual bridge. Answer Explanation: The answer 'swaying' means something that is moving slowly from one side to the other. In this case, it describes floors or platforms that were not still. Reason For Correctness: The correct answer is 'swaying' because the passage describes the tests engineers conducted to understand the bridge's movement. It says that they made measurements in labs where people walked on 'swaying platforms'. The word 'platforms' in the passage is similar to 'floors' in the summary question. |
| Q20 | further apart | "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" | Excerpt/Passage Explanation: The passage says that when people walk on a surface that is moving from side to side, they try to keep their balance by moving their legs wider apart. Answer Explanation: The answer means that people move their legs away from each other, making the space between their feet bigger. Reason For Correctness: The correct answer is 'further apart' because the passage explains the natural way people react to a moving surface to stay balanced. The passage states that on a 'swaying surface', people 'compensate and stabilise themselves by spreading our legs further apart'. The summary asks what people do with their legs to 'keep balance when the floor is shaking', which directly matches this information. |
| Q21 | footsteps | It is an unconscious tendency for pedestrians to match their footsteps to the sway, thereby exacerbating it even more | Excerpt/Passage Explanation: The passage says that people walking on the bridge (pedestrians) naturally start to change their steps (their footsteps) to move in the same way as the bridge is shaking (the sway). They do this without thinking about it, and this action makes the shaking problem bigger. Answer Explanation: The answer 'footsteps' means the steps a person takes when they are walking. Reason For Correctness: The correct answer is 'footsteps' because the passage explains what an engineer named Pat Dallard believes. He states that people walking on the swaying bridge, without realizing it, start to move their feet in the same rhythm as the bridge's movement. The summary sentence mentions that pedestrians adjust something to match the sway, and the passage explicitly says they 'match their footsteps to the sway'. |
| Q22 | horizontal forces | 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 | Excerpt/Passage Explanation: The passage says that a professor named Fujino Yozo thinks that the sideways power from people walking, running, or jumping can cause the bridge to shake a lot from side to side. 'Horizontal forces' means power that pushes sideways. Answer Explanation: The answer 'horizontal forces' means the sideways pushes or energy that people create when they move. Reason For Correctness: The correct answer is 'horizontal forces' because the summary asks what Professor Fujino Yozo's study found could cause the bridge's vibration. The passage directly states that Professor Fujino Yozo believes that the 'horizontal forces' created by people 'walking, running or jumping' were the cause of the excessive shaking. |
| Q23 | upright | 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 | Excerpt/Passage Explanation: The passage says that when more and more people started walking with the same rhythm, the bridge swayed very much. It swayed so much that people had to stop walking because they could not stand up straight. Answer Explanation: The answer means to stand straight on your feet, without falling over. Reason For Correctness: The correct answer is 'upright' because the passage describes what happened when the bridge's swaying became too strong. According to Professor Fujino Yozo's study, people walked in the same rhythm as the swaying bridge, which made the movement worse. This continued until people could no longer stand straight and had to stop walking. |
| Q24 | Arup | 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 | Excerpt/Passage Explanation: The passage says that the engineering company Arup started a research program. They needed to measure the force of people walking on the bridge, which means they needed data with numbers. The passage then explains that while some books talked about the problem, none of them provided specific numbers ("quantifies the force"). This means Arup discovered there was not enough useful data to help them design a solution. Answer Explanation: The answer is "Arup". Arup is the name of the engineering company that was in charge of building the bridge. Reason For Correctness: The correct answer is Arup because this was the company that started a research project to fix the bridge's wobble. During their research, they found that there was not enough information, or data, available to help them. The passage states that information in existing books did not "quantify the force", which means there were no exact numbers about how people walking could make the bridge move. This lack of information is what "not enough data collection" refers to. |
| Q25 | Imperial College | 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 | Excerpt/Passage Explanation: The passage says that the special floor used for the test at Imperial College was 'too short'. Because it was not long enough, they could only measure a few steps at a time. Answer Explanation: The answer is 'Imperial College'. This is the name of a university that did tests to understand why the bridge was shaking. Reason For Correctness: The correct answer is 'Imperial College' because the passage describes the tests this university performed. The passage says that the platform, or special floor, they used for testing was 'too short'. This directly matches the problem described in the table as 'Not long enough'. |
| Q26 | University of Southampton | The tests at the University of Southampton involved a person walking on the spot on a small shake table the "walking on the spot" test did not accurately replicate forward walking, although many footsteps could be observed using this method |
Excerpt/Passage Explanation: The passage says that the University of Southampton's test had a person walking in one place. The passage then explains that this method was not like real, forward walking. Answer Explanation: The answer is the name of a university in England that helped to study the bridge problem. Reason For Correctness: The correct answer is "University of Southampton" because the passage states this university conducted a test where a person was "walking on the spot". The passage then explains that this test was not realistic because it "did not accurately replicate forward walking". This matches the problem described in the table as "Not like the real walking experience". |