The Bridge that Swayed IELTS Reading Answers & Translation

In June 2000, the newly inaugurated London Millennium Footbridge was forced to close just two days after opening due to unexpected and violent lateral swaying. This incident not only turned a proud architectural achievement into a media laughingstock—earning it the nickname “the wobbly bridge”—but also presented an unprecedented challenge for structural engineers.

The reading passage The Bridge That Swayed guides learners through an investigation that reads like a technical detective story: from initial blame placed on wind-catching flags to the discovery of a fascinating crowd dynamics phenomenon, where the human subconscious reflex to maintain balance inadvertently synchronized and amplified the bridge’s vibrations. For IELTS candidates, this is an exemplary text on applied science and structural physics, requiring the ability to parse experimental data and distinguish between the specific limitations of various laboratory testing methods.

Reading Passage

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 a 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 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 a 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 organizations.

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 Which FOUR of the following could be seen on the day when the bridge opened to the public? Choose FOUR letters, A-I, and write your answers in boxes 14-17 on your answer sheet.

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 synchronized 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. The bridge was closed shortly after the opening ceremony

Questions 18 – 23 Complete the summary below. Choose NO MORE THAN TWO WORDS from the passage for each answer. Write your answers in boxes 18-23 on your answer sheet.

Why the Millennium Bridge Swayed

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 a series of tests were conducted on how people walk on 19. _______________ floors.

The tests showed people would place their 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 Complete the table below. Choose NO MORE THAN THREE WORDS from the passage for each answer. Write your answers in boxes 24-26 on your answer sheet.

Full Reading Passage Translation

When the Millennium footbridge in London was inaugurated in June 2000, it swayed alarmingly. This generated significant public attention, and the bridge became known as London’s “wobbly bridge.”

The Millennium Bridge was the first new bridge across the River Thames in London since Tower Bridge opened in 1894, and it was the first designed exclusively for pedestrians. The bridge connects the City of London near St Paul’s Cathedral with the Tate Modern art gallery on Bankside.

The bridge initially opened on Saturday, June 10, 2000. During the opening ceremony, a crowd of over 1,000 people gathered on the southern half of the bridge, led by a band. As they began to walk across to the music, an unexpectedly pronounced lateral movement of the bridge deck occurred. “It was a beautiful day, and the bridge was on the route of a major charity walk,” one pedestrian recounted. “At first, it was still. Then it began to sway sideways, just slightly. Then, almost from one moment to the next, as large groups of people crossed, the wobbling intensified. Everyone had to stop walking to maintain their balance, and sometimes they had to hold onto the handrails for support.”

It was immediately decided to limit the number of people on the bridge, and the media dubbed it the “wobbly” bridge, declaring it another high-profile failure of a British Millennium Project. To fully investigate and resolve the issue, the decision was made to close the bridge on June 12, 2000.

Arup, the lead member of the committee responsible for the bridge’s construction, decided to tackle the issue head-on. They immediately launched a fast-track research project to find the cause and a solution. The embarrassed engineers found a videotape from that day showing the center span swaying about 3 inches sideways every second and the south span swaying 2 inches every 1.25 seconds. Because there was a significant wind blowing during the opening days (force 3-4) and the bridge was decorated with many large flags, the engineers initially thought that the wind might be exerting excessive force on the flags and banners. However, it was quickly concluded that wind buffeting did not contribute significantly to the bridge’s vibration. Nevertheless, after measurements were taken in university laboratories regarding 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 theory were developed.

This unexpected motion was the result of a natural human reaction to small lateral movements. It is well known that a suspension bridge tends to sway when troops march across 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 stabilize ourselves by spreading our legs further apart, but this increases the lateral push.” Pat Dallard, an engineer at Arup, stated that you change your walking style to match the bridge’s movement. It is an unconscious tendency for pedestrians to synchronize their footsteps with the sway, thereby exacerbating the situation. “It’s quite like walking on the deck of a rolling ship; you move one way and then the other to compensate for the roll.” The way people walk does not necessarily have to match the bridge’s natural frequency exactly, as in resonance; the interaction is more subtle. As the bridge moves, people adjust their walking style in their own way. The problem is that when there are enough people on the bridge, the total sideways push can exceed the bridge’s ability to absorb it. The movement becomes excessive and continues to increase until people find it difficult to walk—they may even have to hold onto the handrails.

Professor Fujino Yozo of the University of Tokyo, who studied the earthquake-resistant Toda Bridge in Japan, believes that horizontal forces caused by walking, running, or jumping can also, in turn, cause excessive dynamic vibration in the bridge’s lateral direction. He explains that as the structure began to move, pedestrians adjusted their gait to the same lateral rhythm as the bridge; these adjusted footsteps magnified the motion, much like when four people stand up in a 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.

To design a method for reducing these movements, an immediate research program was launched by the bridge’s engineering designer, Arup. It was decided that the force exerted by pedestrians had to be quantified and related to the bridge’s motion. Although there were some descriptions of this phenomenon in existing literature, none actually quantified the force. Therefore, there was no quantitative analytical method to design the bridge against this effect. The efforts to solve the problem quickly received support from several universities and research organizations.

Tests at the University of Southampton involved a person walking on the spot on a small shake table. Tests at Imperial College involved people walking along a specially built 7.2m-long platform that could be driven laterally at different frequencies and amplitudes. These tests had their own limitations. While the Imperial College test platform was too short, allowing only seven or eight steps to be measured at once, 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 the influence of other people in a crowd on the behavior of the individual being tested.

The results of the laboratory tests provided information that enabled the initial design of a retrofit to proceed. However, unless the bridge’s usage was to be greatly restricted, only two generic options to improve its performance were considered feasible. The first was to increase the bridge’s stiffness to move all its lateral natural frequencies out of the range that could be excited by lateral footfall forces, and the second was to increase the bridge’s damping to reduce the resonant response.

Academic Vocabulary Summary

• Pedestrians (n): People walking.

• Pronounced lateral movement (phrase): Significant/strong side-to-side movement.

• Wobble / Sway (v/n): To move unsteadily from side to side.

• Exerting excessive force (phrase): Applying an overly strong force.

• Wind buffeting (n): The impact or shaking caused by wind.

• In lockstep (idiom): Moving in perfect unison (like soldiers marching).

• Exacerbating (v): Making a problem worse.

• Oscillation / Vibration (n): The act of swinging or shaking back and forth.

• Quantified (v): Measured or expressed as a specific quantity.

• Retrofit (n/v): A structural improvement or upgrade added to an existing system.

Reading Answer Key Suggestions

Questions 14 – 17: Multiple Response

B. The bridge swayed from side to side -> CORRECT (Paragraph 3 states: “there was immediately an unexpectedly pronounced lateral movement of the bridge deck” and witness accounts: “it began to sway sideways, just slightly