Learning lessons from London’s wobbly bridge

Almost everyone can remember seeing the newly-opened London Millennium footbridge swaying alarmingly from side to side. This surprisingly common phenomenon led James Brownjohn, Professor of Structural Dynamics at the University of Sheffield to embark on a vital study into the nature of loading due to crowds of pedestrians.

To mark the Millennium, a new footbridge was built across the River Thames in London. When the bridge was opened it started to sway wildly with enough sideways movement to make people stop walking and hold on to the hand-rails for safety. Londoners soon nicknamed it the wobbly bridge and it had to be closed and modified over an 18 month period to eliminate the wobble entirely.

But the famous example of the London Millennium footbridge is only the tip of the iceberg. "There are telling examples, many of which do not reach the public domain, of highly expensive industrial or experimental facilities that are unfit for purpose due to pedestrian dynamic loading caused by walking," says Professor Brownjohn of the Department of Civil and Structural Engineering.

The problem is that the guidance to structural designers on the nature of dynamic loads caused by walking and running is at best rudimentary and simplistic, and at worst inaccurate. Moreover, there are no formal guidelines on the loading due to groups or crowds of pedestrians and this lack of understanding may be financially disastrous or even fatal.

"This is because the dynamic forces induced by humans, such as walking and running are random in nature, difficult to predict and even more difficult to use in design practice," says Professor Brownjohn adding, "However, many examples have indicated the need to deal with this problem."

What is required is a viable database of a large number of loading records of walking and running which will help ensure the safety of any new structure. Professor Brownjohn is now working on a project to build this database. Such databases have been set up for earthquake records, but never for this kind of dynamic loading.

Entitled 'Human walking and running forces: novel experimental characterisation and application in civil engineering dynamics', the project will run for three years up to 2009 and is funded by £300,000 from the Engineering and Physical Sciences Research Council. It will provide evidence for better structure design by taking two approaches.

"As dynamic forces induced by humans are generated by acceleration and deceleration of human body mass, we will measure movement of the human body or bodies and compare them with standard direct measurement of forces on a treadmill to build up a database. Then we will use the established database to develop models of these forces which can be applied to simulate dynamic response of real-life structures," says Professor Brownjohn.

With a better understanding of pedestrian loading under all conditions, the next generation of pedestrian loading models can be developed, leading to greater confidence in the design of floors and footbridges.


For further information, please contact Professor James Brownjohn at:

tel: 0114 222 5771

email : james.brownjohn@sheffield.ac.uk