Synopsis
This paper starts by describing the structure of the London Millennium Footbridge.
The bridge opened on 10 June 2000. During the opening day unexpected lateral movements occurred as pedestrians crossed the bridge. The paper describes the events of opening day and the research and analysis that were carried out as a result of these movements.
The lateral force exerted by pedestrians on the moving deck surface is found to be related to the movement. The results show that the phenomenon is not related to the technical innovations of the bridge and that the same phenomenon could occur on any bridge with a lateral frequency below about 1.3Hz loaded with a sufficient number of pedestrians. A selection of other bridges, including one road bridge, found to have exhibited the same phenomenon, are listed.
The paper describes the development of a retrofit to control the vibrations. This involves the use of fluid-viscous dampers and tuned mass dampers to achieve damping levels in excess of 20% of critical. The results of tests on the bridge with a prototype installation of a small number of the proposed dampers are presented, which show that the performance of the damping scheme conforms with analytical predictions.