A joint project of:
Structures Group (A. McRobie, G. Morgenthal) and
       Signal Processing Group (J. Lasenby, M. Ringer, S. Gamage)

Coverage #1: NCE
Coverage #2: CUED 125 (flash and simplified)
Coverage #3: Prof. Brian Josephson, Cambridge
Coverage #4: Radio 4 interview, 10/8/2000 (available here soon)
Coverage #5: Libby Purves in The Times, 15/8/2000 + cartoon
Ove Arup's official Millennium Bridge website
 

THE STRUCTURE AND OUR SIMULATION Like any suspension bridge the Millennium Bridge is very flexible. It has many modes of oscillation. Our simulator recreates one of these modes, and can be readily adjusted to simulate others.     structural mode of vibration excited by the people Our simulator is similar to the “section models” we study in the wind tunnel where the interesting physics is in the fluid. Here the interesting physics is actually biology, the behaviour of people on the bridge. It is difficult to make scale models of people, so we have had to make our model full-scale. mechanism represented by our model THE BASIC PHYSICS AND BIOLOGY The large oscillations experienced by the Millennium Bridge are caused by a novel phenomenon of human-structure phase locking.  It is this phenomenon that we are studying in this experiment. Small random vibrations of the bridge are sufficient to cause large numbers of people to walk in step, so reinforcing the motion. It is positive biofeedback. It is NOT the old chestnut about troops needing to break step. Even if troops broke step they would soon be back in step. They cannot help it.

STUDYING THE HUMAN-STRUCTURE INTERACTION The first phase of the experiment is the study of a single person walking (on a treadmill) on the simulator using motion capture equipment developed at CUED. - Bright markers are placed both on the bridge and on the person and are observed with three CCD cameras. - Data from the cameras over some time period is stored in real-time via a framegrabber and PC. - The cameras are then calibrated (we work out where they are) which enables us to track the data and create a 3D reconstruction.     The view of the markers on the walker’s legs and the rig from the three cameras  Generic humanoid mapped to the 3-dimensional reconstruction of the walking motion We can then view (from any angle) the complex interactions between human and bridge. Moreover, we can make quantitative studies of gait vs. time, gait vs. bridge oscillation (with various damping values) etc. The next phase will be to investigate the interactions when multiple people walk on our bridge.

ASSOCIATED PHYSICS AND BIOLOGY Although a new phenomenon in the design of footbridges, phase synchronisation is a familiar phenomenon throughout the physical and biological sciences – for example: At dusk, swarms of Pteroptyx malaccae fireflies move from random to synchronous flashing along the river-banks of Malaysia (see David Attenborough's 'The Trials of Life') Male fireflies flashing in unison - Arrays of superconducting Josephson junctions move from random to synchronous oscillation (at 1010 Hz) - The moon always points the same face towards the Earth - Menstrual cycles of women in prison and in convents phase-lock - The phase-locking of two pendulum clocks on a shelf was noticed by Huyghens over 300 years ago. - Vortices shed into the wake of a flexible cylinder phase-lock if the frequency of shedding is close to the natural frequency of the cylinder. There are many more examples.

please email questions and comments to Guido Morgenthal or Allan McRobie.

last modified 06/01/2003, hits since then: