Abstract Summary
Vibration serviceability under human-induced loading has become a key design criterion when determining the structural shape and dimension of footbridges. Over the last two decades, the vibration serviceability of footbridges under walking excitation has been widely investigated. However, little to no attention has been paid to running actions as a design load. The concerns about the impact of dynamic running actions (single person or in group) have grown significantly as (1) the involved load amplitudes are significantly higher than for walking, (2) the dominant frequency spectrum is different from walking and (3) footbridges are progressively more exposed to running due to the increased focus on a healthy lifestyle. So far, however, no expertise is available on running excitation as a load scenario for civil engineering structures. The state of the art involving dynamic running actions is limited to single-person load models valid for running on a rigid laboratory floor. The load model presented by currently available standards and design guidelines represents a single or a small group of runners as perfectly periodic and perfectly synchronized individuals. The structural response is then calculated assuming resonant conditions with each of the relevant structural modes. These unwarranted assumptions risk to lead to unrealistically high predicted vibration levels that compromise any slender structural design or require the installation of expensive vibration mitigation devices. The development of realistic load scenarios for running excitation requires input on (1) intra-person variabilities, (2) inter-person variabilities and (3) human-structure interaction phenomena specifically for the running actions, and their impact on the resulting structural response. In this contribution, it is first shown how vibration measurements on the lower back of a running person can be used to reconstruct the vertical dynamic running load. Second, this technique is used to collect information on the in-field running behavior of individuals and groups. This data is then used to identify and characterize intra- and inter-person variabilities of the dynamic running load. Based on these results, the impact of these variabilities on the resulting structural response is investigated numerically. Finally, recommendations are formulated for further research and development of procedures for the vibration serviceability assessment of footbridges under dynamic running actions.
