Academic Reading Test 22.2

READING PASSAGE 2

You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2 below.

 

London Swaying Footbridge

 

A.  In September 1996 a competition was organized by the Financial Times in association with the London Borough of Southwark to design a new footbridge across the Thames. [Crack IELTS with Rob] The competition attracted over 200 entries and was won by a team comprising Arup (engineers), Foster and Partners (architects) and the sculptor Sir Anthony Caro. 


B. The bridge opened to the public on 10 June 2000. Up to 100,000 people crossed it that day with up to 2000 people on the bridge at any one time. At first, the bridge was still. Then it began to sway just slightly. [Crack IELTS with Rob] Then, almost from one moment to the next,  when large groups of people were crossing, the wobble intensified. This movement became sufficiently large for people to stop walking to retain their balance and sometimes to hold onto the handrails for support. It was decided immediately to limit the number of people on the bridge, but even so, the deck movement was sufficient to be uncomfortable and to raise concern for public safety so that on 12 June the bridge was closed until the problem could be solved.


C. The embarrassed engineers found the videotape that day which showed the center span swaying about 3 inches side to side every second. The engineers first thought that winds might be exerting excessive force on the many large flags and banners bedecking the bridge for its gala premiere. [Crack IELTS with Rob] What’s more, they also discovered that the pedestrians also played a key role. Human activities, such as walking, running, jumping, swaying, etc. could cause horizontal force which in turn could cause excessive dynamic vibration in the lateral direction in the bridge. 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 a small boat at the same time. As more pedestrians locked into the same rhythm, the increasing oscillations led to the dramatic swaying captured on film.


D.  In order to design a method of reducing the movements, 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. [Crack IELTS with Rob] So there was no quantitative analytical way to design the bridge against this effect. An immediate research program was launched by the bridge's engineering designer Ove Arup, supported by a number of universities and research organizations.


E. 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 with a specially built, 7.2m-long platform which could be driven laterally at different frequencies (n and amplitudes. Each type of test had its limitations. [Crack IELTS with Rob] The Imperial College tests were only able to capture 7-8 footsteps, and the ‘walking on the spot’ tests, although monitoring many footsteps, could not investigate normal forward walking. Neither test could investigate any influence of other people in a crowd on the behavior of the individual being tested.


F.  The results of the laboratory tests provided information which enabled the initial design of a retrofit to be progressed. However, the limitations of these tests was clear and it was felt that the only way to replicate properly the precise conditions of the Millennium Bridge was to carry out crowd tests on the bridge deck itself. [Crack IELTS with Rob] These tests done by the Arup engineers could incorporate factors not possible in the laboratory tests. The first of these was carried out with 100 people in July 2000. The results of these tests were used to refine the load model for the pedestrians. The second series of crowd tests were carried out on the bridge in December 2000. The purpose of these tests was to further validate the design assumptions and to load test a prototype damper installation. The test was carried out with 275 people.


G. Unless the usage of the bridge was to be greatly restricted, only two generic options to improve its performance were considered feasible. [Crack IELTS with Rob] 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 - 15

Choose TWO letters, A-E.

Write the correct letters in boxes 14-15 on your answer sheet.

Which TWO of the following situation were first witnessed during the opening ceremony of the bridge?

  • All the engineers went to see the ceremony that day.
  • The frequency of oscillation increased after some time.

15-hide

  • Unexpected sideway movement of the bridge occurred.
  • Vertical movement of the bridge occurred.
  • The design of the bridge astonished the people.

Questions 16 - 17

Choose TWO letters, A-E.

Write the correct letters in boxes 16-17 on your answer sheet.

Which TWO of the following situation were also witnessed during the opening ceremony of the bridge?

  • The bridge fell down when people tried to retain their balance.
  • Pedesfrians had difficulty in walking on the deck.

17-hide

  • It was raining when the ceremony began.
  • The bridge vibrated when a group of people walking on.
  • Vibration could be detected on the deck by the pedestrians.

Questions 18 - 22

Complete the summary below.

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

Write your answers in boxes 18-22 on your answer sheet.

 

  • After the opening ceremony, the embarrassed engineers tried to find out the reason for the bridge's wobbling. Judged from the videotape, they thought that (18,

    WINDS
  • and (19)  might create an excessive force on the bridge. 

    THE PEDESTRIANS
  • The distribution of (20)  resulted from human activities

    HORIZONTAL FORCES
  • could cause (21)  throughout the structure.

    EXCESSIVE DYNAMIC VIBRATION
  • This swaying prompted people to start adjusting the way they walk, which in turn reinforced the (22.

    MOTION
  • After the opening ceremony, the embarrassed engineers tried to find out the reason for the bridge's wobbling. Judged from the videotape, they thought that (18,

    WINDS
  • and (19)  might create an excessive force on the bridge. 

    THE PEDESTRIANS
  • The distribution of (20)  resulted from human activities

    HORIZONTAL FORCES
  • could cause (21)  throughout the structure.

    EXCESSIVE DYNAMIC VIBRATION
  • This swaying prompted people to start adjusting the way they walk, which in turn reinforced the (22.

    MOTION

Questions 23 - 26

Complete the table below.

Choose NO MORE THAN THREE WORDS from Reading Passage 2 for each answer. 

Write your answers in boxes 23-26 on your answer sheet.

 

             Research programs launched by universities and organizations

 

  • Universities/People
    Test at (23 : Limited ability to have 7-8 footsteps

     

    IMPERIAL COLLEGE
  • Walking on the spot' at Southampton: Not enough data on (24

     

    NORMAL FORWARD WALKING
  • Crowd test conducted by (25:

     

    THE ARUP ENGINEERS
  • Aim to verify (26

     

    THE DESIGN ASSUMPTIONS
Result: / Exit

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