Featured Research

from universities, journals, and other organizations

Explaining Why The Millennium Bridge Wobbled

Date:
November 3, 2005
Source:
Cornell University
Summary:
Steven Strogatz, professor of theoretical and applied mechanics at Cornell University, describes the Millennium Bridge's notorious opening-day oscillations in the Nov. 3 issue of Nature.

The notorious opening-day oscillations of London's Millennium Bridge are examined in the Nov. 3 issue of Nature.
Credit: Image courtesy of Cornell University

Steve Strogatz has a penchant for things that happen in unison. So when the Cornell University professor of theoretical and applied mechanics (and author of the 2003 book "Sync: The Emerging Science of Spontaneous Order") heard that thousands of pedestrians had caused London's Millennium Bridge to rock from side to side on its opening day, he was intrigued.

Related Articles


Before the bridge across the River Thames opened, designers hailed it as "a pure expression of engineering structure." They compared its sleek look to a blade of light. Engineers called it "an absolute statement of our capabilities at the beginning of the 21st century."

But it's what happened on opening day that is the subject of Strogatz' Nov. 3 Nature paper.

The Millennium Bridge, a 320-meter-long lateral suspension bridge connecting London's financial district to Bankside, south of the river, opened June 10, 2000. Thousands of pedestrians streamed over it.

At first, the bridge was still. Then it began to sway, just slightly.

Then, almost from one moment to the next, the wobble intensified. And suddenly, people were walking like tentative ice skaters: planting their feet wide, pushing out to the side with each step. Left, right, left, right, in near-perfect unison.

The synchrony was utterly unintentional. But it was those unchoreographed footfalls, says Strogatz, that were responsible for turning a $32 million design triumph into a very embarrassing engineering quandary. The bridge was closed almost immediately.

Strogatz, who has studied the collective behavior of biological oscillators from neurons to fireflies, describes each of the factors that contributed to the bridge's swaying in his paper. Cornell graduate student Daniel Abrams is one of the paper's co-authors.

The problem, says Strogatz, was one of crowd dynamics as much as engineering. The bridge surpassed standards for withstanding weight and wind. Every nonhuman element had been tested.

Instead of focusing on the structure, Strogatz examines the strange phenomenon of people unknowingly working together, simply by walking.

The military has known for years that troops marching in step can create enough vertical force to destroy a bridge. It is standard practice for soldiers to break step at every bridge crossing.

But the Millennium Bridge problem is not quite the same, says Strogatz. In this case, the movement was lateral, not vertical. More importantly, the people were just pedestrians. No one was trying to walk in step; pedestrians did so only to accommodate the bridge's movement under their feet.

But which came first, the bridge's movement or the synchronous strides? And what set the whole thing off?

"It's a chicken-and-egg problem," says Strogatz. "That's what our paper explains." From the beginning, the bridge had two factors working against it: It was by design a flexible structure, and its natural frequency is close to that of human walking. From there, Strogatz says, all it needed was a relatively small crowd to spark the wobble.

"If the people are initially disorganized and random, if a few of them get into sync by accident, the bridge would become unstable," he says. With a certain critical number of pedestrians, the wobbling becomes marked enough to force everyone into stride -- thus compounding the problem.

And the critical number of pedestrians, tested subsequently on the Millennium Bridge and derived independently by Strogatz and co-authors, is as low as 160. An estimated 80,000 people crossed the bridge on opening day, with as many as 2,000 on it at any one time.

"I'm not a civil engineer. I know nothing about bridges," says Strogatz. "What I do know is group behavior. That was our contribution."

The Millennium Bridge reopened in 2002 after engineers fitted it with 91 dampers to absorb both lateral and vertical oscillations. The modifications cost about $8.9 million.

If Strogatz' analysis is correct -- "and we hope someone will test it," he says -- engineers will be able to use it to prevent such expensive, embarrassing and possibly dangerous fiascos in the first place.

"They could solve the problem before they build it," says Strogatz. "That's what this theory will do."

In addition to Abrams, the paper, "Crowd Synchrony on the Millennium Bridge," was authored by Allan McRobie of the University of Cambridge; Bruno Eckhardt of Fachbereich Physik, Philipps-Universitδt, Marburg, Germany; and Edward Ott of the University of Maryland. Eckhardt and Ott solved the problem independently for the same result.


Story Source:

The above story is based on materials provided by Cornell University. Note: Materials may be edited for content and length.


Cite This Page:

Cornell University. "Explaining Why The Millennium Bridge Wobbled." ScienceDaily. ScienceDaily, 3 November 2005. <www.sciencedaily.com/releases/2005/11/051103080801.htm>.
Cornell University. (2005, November 3). Explaining Why The Millennium Bridge Wobbled. ScienceDaily. Retrieved November 26, 2014 from www.sciencedaily.com/releases/2005/11/051103080801.htm
Cornell University. "Explaining Why The Millennium Bridge Wobbled." ScienceDaily. www.sciencedaily.com/releases/2005/11/051103080801.htm (accessed November 26, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Wednesday, November 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

NASA's First 3-D Printer In Space Creates Its First Object

NASA's First 3-D Printer In Space Creates Its First Object

Newsy (Nov. 26, 2014) — The International Space Station is now using a proof-of-concept 3D printer to test additive printing in a weightless, isolated environment. Video provided by Newsy
Powered by NewsLook.com
Bolivian Recycling Initiative Turns Plastic Waste Into School Furniture

Bolivian Recycling Initiative Turns Plastic Waste Into School Furniture

Reuters - Innovations Video Online (Nov. 26, 2014) — Innovative recycling project in La Paz separates city waste and converts plastic garbage into school furniture made from 'plastiwood'. Tara Cleary reports. Video provided by Reuters
Powered by NewsLook.com
Blu-Ray Discs Getting Second Run As Solar Panels

Blu-Ray Discs Getting Second Run As Solar Panels

Newsy (Nov. 26, 2014) — Researchers at Northwestern University are repurposing Blu-ray movies for better solar panel technology thanks to the discs' internal structures. Video provided by Newsy
Powered by NewsLook.com
Today's Prostheses Are More Capable Than Ever

Today's Prostheses Are More Capable Than Ever

Newsy (Nov. 26, 2014) — Advances in prosthetics are making replacement body parts stronger and more lifelike than they’ve ever been. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins