IELTS® Academic Reading Practice 68

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Why the Millennium Bridge 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 12 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 both 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 arc required to break step when crossing such a bridge. “If we walk on a swaying surface we tend to compensate and stabilize 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, Arup, the bridge’s engineering designer immediately launched a research program. 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 organizations.

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.




This reading practice simulates one part of the IELTS Academic Reading test. You should spend about twenty minutes on it. Read the passage and answer questions 14-26.
Questions 14-17
Complete each sentence with the correct ending A-H from the box below.

Write the correct letter A-H in boxes 14-17 on your answer sheet.

NB You may use any letter more than once.

  1. engineers thought that large flags on the bridge were responsible
  2. people adjusted the way they walked
  3. the same phenomenon occurred
  4. the bridge began to move from side to side
  5. there was a strong possibility of collapse
  6. the phenomenon was described in literature
  7. walking along a specially designed structure
  8. the structure built up a strong up and down movement

14. When people started crossing

15. Because of the strong winds

16. When a body of troops crossed a bridge marching in step

17. Research into the phenomenon involved

Questions 18-23
Complete the summary below.

Choose NO MORE THAN THREE WORDS from the passage for each answer.

Write your answers in 18-23 on your answer sheet.

In order to understand why the Millennium bridge swayed, engineers studied a tape of the opening ceremony and instigated a straight away. Engineers originally believed that the lateral movement was caused by the wind’s effect on the many flying that day. However, later studies, based on how people walk on moving platforms, meant that a  was reached. The tests showed that people walking on a swaying surface tend to compensate by taking longer strides which increases the , this in turn makes the sway worse. A study by Professor Fujino Yozo found that vibration from people moving caused high in the sideways movement of the bridge. They would then change their , causing the structure to move even more.

Questions 24-26
Complete the table using the list of words, A-C, below.
  1. Imperial college
  2. Professor Fujino Yozo
  3. Pat Dallard
Said by Statements
The structure moves because of users changing their walk to fit the same sideways sway as the bridge. This helps exacerbate the movement even more.
Sideways movement becomes a problem when there is more lateral impact than the bridge can take.
The tests were found to have shortcomings in that insufficient steps could be measured and these did not duplicate the action of walking forward.



Answer Sheet
1
N/A
2
N/A
3
N/A
4
N/A
5
N/A
6
N/A
7
N/A
8
N/A
9
N/A
10
N/A
11
N/A
12
N/A
13
N/A
14
15
16
17
18
19
20
21
22
23
24
25
26
27
N/A
28
N/A
29
N/A
30
N/A
31
N/A
32
N/A
33
N/A
34
N/A
35
N/A
36
N/A
37
N/A
38
N/A
39
N/A
40
N/A


Reading Passage Vocabulary
Why the Millennium Bridge 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 12 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 both 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 arc required to break step when crossing such a bridge. “If we walk on a swaying surface we tend to compensate and stabilize 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, Arup, the bridge’s engineering designer immediately launched a research program. 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 organizations.

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.

 
IELTS Academic Reading Tips for Success
These are general tips that will appear on all reading questions.

Tips to improve your reading speed
To get a high score on the IELTS reading section, you need to have a fast reading speed. To have a fast reading speed, you need to improve your vocabulary and practice dissecting sentences. One strategy to dissect a sentence is to look for the subject and verb of the sentence. Finding the subject and verb will help you better understand the main idea of said sentence. Keep in mind, a common feature of a IELTS reading passage is to join strings of ideas to form long compound sentences. This produces large chunks that students have a hard time absorbing. Do not get overwhelmed by its length, just look for the subject and verb, the rest of the ideas will flow.


Keep in mind, having a slow reading speed makes skimming or scanning a reading passage more difficult. The process of quickly skimming through a reading passage for specific keywords or main ideas is a requirement for you to employ successful reading strategies to improve your IELTS reading score. In other words, skimming and scanning are critical skills to ensure you complete all questions in the allotted time frame.
IELTS Reading Strategies
Once you can read and comprehend a passage with a rate of, at least, 220 words per minute, you'll be ready to start implementing our strategies. All too often, students spend too much time reading the passages and not enough time answering the questions. Here is a step by step guide for tackling the reading section.

  1. Step 1: Read questions first

    One of the most common mistakes that candidates make when approaching the reading exam is reading every single word of the passages. Although you can practice for the exam by reading for pleasure, "reading blindly" (reading without any sense of what the questions will ask) will not do you any favors in the exam. Instead, it will hurt your chances for effectively managing your time and getting the best score.

    The main reason to read the questions first is because the type of question may determine what you read in the passage or how you read it. For example, some question types will call for the "skimming" technique, while others may call for the "scanning" technique.

    It is important to answer a set of questions that are of the same question type. You'll need to determine which question type you want to tackle first. A good strategy would be to start with the easier question type and move on to more difficult question types later. The Easiest question types are the ones where you spend less time reading. For example, the Matching Heading question type is an easier one because you only need to find the heading that best describes the main idea of a paragraph. An example of a difficult question type would be Identifying Information. For this question type, you'll need to read each paragraph to find out if each statement is TRUE, FALSE, or NOT GIVEN according to the passage.

    Here is a table that lists the difficulty levels for each question type. Use this table as a reference when choosing which question type you want to tackle first.


    Difficulty level Question Type
    Easy Sentence Completion
    Short answer
    Medium Matching Features
    Multiple choice
    Matching Headings
    Summary, Table, Flow-Chart Completion
    Difficult Matching Sentence Endings
    Matching Information
    Identifying Information (TRUE/FALSE/NOT GIVEN)
    Identifying Viewer's claims (YES/NO/NOT GIVEN)

  2. Step 2: Read for an objective

    After you've read the questions for the passage, you will be able to read for an objective. What does this mean? For example, if you come across a question that includes the year "1896", you can make a note of when this year comes up in the text, using it to answer the question later on. There are two reading techniques that will help you stay on track with reading for an objective. The first one, skimming, is best defined as reading fast in order to get the "gist", or general idea, or a passage. With this technique, you are not stopping for any unfamiliar words or looking for specific details. The second technique, scanning, is best defined as reading for specific information. With this technique, you are not reading for the overall gist, but rather, specific information. Notice how each of these techniques has a specific objective in mind. This will help you find information more quickly.

  3. Step 3: Take notes

    As you're reading for an objective, you should also be making notes on the margins of the passage, placing stars next to key information, or underlining things that you believe will help you answer the various questions. This will make it easier for you to check back when you are asked certain things in the questions. Choose whichever note-taking system is right for you - just make sure you do it!

  4. Step 4: Answer wisely

    After you've read the questions, read the passage, and have taken any appropriate notes, you you should have located the part of the text where you where you need to read carefully. Then just read carefully and think critically to determine the correct answer.

IELTS Reading Question Types
 
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