Quantification of human-structure interaction

Abstract

In lightweight structural systems there is increasing evidence that the presence of humans influences the dynamics characteristics of the system. In the past, most effort on determining the footfall-induced vertical force to the walking surface has been conducted using rigid or non-flexible surfaces such as treadmills. However, should the walking surface be vibrating, the characteristics of human walking could change to maximize comfort. This interaction between the structure and human may account for the discrepancy between the levels of vibration predicted by theory and those observed in practice. Indeed, many design rules can be seen to be conservative, perhaps partly because knowledge of this human-structure interaction is limited. This work aims to address this problem by quantifying the magnitude of human-structure interaction through a comprehensive experimental programme. Novel experimental techniques are used to measure the human-imparted force on the walking surface. Both rigid and flexible (vibrating) surfaces are used, and we measure the imparted vibration response on a lively footbridge (the Warwick Bridge) which acts as the flexible surface. A range of test subjects is considered, walking at a range of pacing frequencies. Comparison is made between a notional vibration response from the footfall force imparted to the rigid surface and the actual vibration response caused by the footfall force imparted to the flexible surface. Key aspects of the experimental regime are also explained. Finally, some comparisons are made using footfall force models from the literature. It is concluded that human-structure interaction is a key phenomenon that should be taken into account in the design and assessment of vibration-sensitive structures.