How did ARUP fix the issue with the Millennium Bridge?
Although a few previous reports of this phenomenon were found in the literature, none of them gave any reliable quantification of the lateral force due to the pedestrians, or any relationship between the force exerted and the movement of the deck surface. Arup therefore carried out tests in 3 universities, as well as crowd walking tests on the bridge itself, in order to quantify the force exerted on the structure. Arup then designed a system of passive dampers which are mobilized by the lateral movements of the bridge. These dampers are arranged beneath the deck over the full length of the bridge, as well as at the piers and at the south abutment. In order to demonstrate that the solution performed satisfactorily, Arup carried out a crowd test with 2000 pedestrians — the most extreme dynamic test ever carried out on a bridge. The bridge movements were less than a sixth of the allowable movements. The bridge reopened in February 2002.
