what is the damping required for The Millennium Bridge?

Question

The Millennium Bridge which was built in 2000

Answer 1

The motion was caused by the human reaction to small lateral movements in the bridge, which set up a driven harmonic motion in the bridge. As such the motion was not anticipated by the computational analysis of the bridge prior to construction. It is often thought that the unusually low profile of the suspension cables contributed to the problem, but an analysis by the structural engineer, Arup, shows that it can occur in any suspension bridge which happens to have the appropriate resonant frequencies. After extensive analysis, the problem was fixed by the retrofitting of 37 fluid-viscous dampers (energy dissipating) to control horizontal movement and 52 tuned mass dampers (inertial) to control vertical movement. This took from May 2001 to January 2002 and cost £5m. After a period of testing the bridge was successfully re-opened on 22 February 2002, and as yet there have not been any noticeable severe vibrations.