Synchronised pedestrian excitation of footbridges

A simple theory, based on the governing differential equations of motion, has been developed for predicting the critical number of pedestrians likely to induce synchronised lateral excitation of footbridges. Detailed prescription of the lateral forces, produced by pedestrians synchronising their motion in response to lateral accelerations of the bridge, is not required. The theoretical prediction is compared, and shows close agreement, with the results of full-scale tests on the London Millennium Footbridge.