Human walking and running forces: Novel experimental characterization and application in civil engineering dynamics

Of all human-induced dynamic excitations, such as jumping, bouncing/bobbing and swaying, dynamic loads induced by humans walking and running are the least understood and most complex to deal with. This is because they change simultaneously in time and space, being random in nature and varying considerably not only between different people but also for a single individual who cannot make two identical consecutive steps. Since these important aspects of pedestrian excitation have not been adequately researched in the past, the resulting lack of knowledge has reflected badly on the quality of mathematical models for walking/running forces. These are indispensable when checking vibration serviceability of slender structures prone to vibrations when occupied and dynamically excited by humans. The problem typically occurs in the case of light-weight footbridges, longspan floors and staircases. The development of better force models which can be used more reliably in structural design requires an adequate experimental and analytical approach to account for their stochastic nature. Present state-of-the-art approach includes utilisation of traditional equipment for direct ground reaction force measurement comprising a force plate or an instrumented treadmill. However, both systems are confined to artificial laboratory environment imposing various restrictions on human movement and thus possibly affecting natural variability of the force records. Therefore, when investigating issues like vibration serviceability there is a growing trend towards monitoring subjects during daily life activities in their natural environment. Having all this in mind, in addition to the direct measurement, this paper presents a novel system that utilises 'free field' measurement of three-component walking/running forces continuously in time. Since the system can estimate the load applied directly to structures, it will enable studies of particular interest and uncertainty in civil structural engineering dynamics, such as stochasticity of human-structure interaction and pedestrian synchronisation when walking/running on perceptibly moving structures.