Section model tests on human – structure lock-in

Abstract

In June/July 2000, shortly after the opening of the London Millennium Bridge, experiments were undertaken on a full-scale section model built to represent a footbridge swaying under pedestrian action. The processes of human–structure interaction and the phenomenon of phase synchronisation were investigated. Various instabilities were observed using 3D motion capture equipment, and lateral forces were inferred from the dynamic response of the rig. Implications for footbridge design are discussed. Of particular concern is the possibility of vertical synchrony. In lieu of detailed experimental data, it is recommended that the existing footbridge stock be surveyed with respect to a dimensionless group, analogous to the Scruton number of wind engineering, for each mode (horizontal, vertical, torsional or general). A graph of an equivalent mass per unit area against frequency could be of use to designers in assessing new designs against the performance of existing structures.