Numerical and experimental study of footbridge vibrations induced by running

The search for the perfect balance of financial, environmental and aesthetic aspects in designing modern footbridges has driven architects and engineers to conceive very slender and lightweight structures. However, this trend has resulted in structures to be increasingly sensitive to vibrations induced by walking and running pedestrians. Over the last two decades, the behavior of footbridges and their vibration serviceability have been widely investigated when excited by walking humans. Numerical models have been developed, which not only are able to accurately characterize human dynamic actions, but which also account for the effects related to human-structure interaction (HSI) and human-human interaction (HHI) in case of crowds. However, less attention has been paid to the case when footbridges are excited by running individuals or groups of runners. As running has become a popular activity, more footbridges are exposed to significantly higher dynamic impacts which, in contrast with walking, can be induced even by a small number of running persons. The aim of this PhD project is to answer to the following acute questions: - How the dynamic actions of a single runner on a slender footbridge can be described and modelled? - How does the vibrating structure affect the behavior of the runner (HSI)? - How can the dynamic actions of groups of running persons, including the effects of HHI, be modelled? In this perspective, the expertise of different fields such as biomechanics (biomechanics of locomotion, analysis and modelling of human gait) and structural mechanics (dynamic behavior of footbridges, human-structure interaction) are combined to develop prediction models for the vibration serviceability of footbridges under running excitation. The PhD research combines both numerical and experimental approaches. Numerical human gait models are exploited to simulate the dynamic actions generated by running and investigated how these are affected by the gait parameters (e.g. stride frequency, leg stiffness). Results are then compared with experimental data coming from real tests both in lab and outdoor. Such experiments involve the use of very accurate research instrumentation such as an instrumented treadmill, gait sensors etc. as well as low-cost sensor technologies which allow on-field tests.