Dynamic loads due to synchronous rhythmic activities of groups and crowds

Predicting vibration performance of civil engineering structures due to human induced rhythmic loading is an increasingly critical aspect of the design process of structures such as sports stadia used for pop/rock concerts, floors accommodating gym and aerobic classes, and footbridges used as spectator galleries during regatta events. Two main reasons for this trend are (1) structures are becoming more slender with improvements in materials and construction techniques and modern trends in architectural design, and (2) groups/crowds are in general becoming livelier than previously was the case, i.e. their activities can become better synchronised due to the presence of various auditory and visual stimuli at above mentioned events. This paper addresses the latter issue by presenting a method to measure human bouncing and jumping forces induced by groups and ultimately crowds using motion capture technology, transferred and adapted from biomedical research. Compared with traditional force platform measurements, the key advantage and novelty of this method is a possibility to measure individual forces of each group/crowd member in natural environments, including real life structures. Constrains imposed by artificial laboratory settings and small size of force plates can significantly affect the quality of the force data. Results show that the new method can be used successfully to study area of significant interest and uncertainty for structural dynamics, particularly synchronisation of individual forces when people bounce and jump in groups on more or less perceptibly moving structures. The new approach presented in this paper is a step towards more thorough and realistic mathematical models of group/crowd rhythmic loading that can be used to simulate more reliably dynamic response, thereby assessing vibration serviceability of above mentioned civil engineering structures convincingly at the design stage.