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Title: Determination of the self-excited forces on structures due to walking pedestrians using a biologically-inspired approach
Author: Bocian, Mateusz
ISNI:       0000 0004 5358 0977
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Vibration serviceability of structures has become an evermore important issue in structural engineering practice. A particularly challenging problem is posed by modelling pedestrian loading on lively structures such as bridges. This is because pedestrians have the capacity to interact with vibrating structures which can lead to amplification of the structural response. However, current design guidelines are often inaccurate and limiting as they do not sufficiently acknowledge this effect and do not allow for consideration of different loading scenarios which might govern the design criteria in different cases. Therefore, this thesis addresses the uncertainty which pertains to the bidirectional pedestrian-structure interaction and its consequences for structural stability. This thesis has three main aims. The first aim is to investigate pedestrian-structure interaction on the ground vibrating in a single lateral and vertical direction by means of a mathematical model. The second aim is to establish a versatile modelling tool for the design of structures against lateral instability due to the loading from crowds with different distributions of defining parameters. The third aim is to evaluate pedestrian actions on laterally-oscillating ground in the laboratory environment while avoiding the implications of artificiality and allowing for unconstraint gait. To achieve these aims a synthetic multidisciplinary biological approach is adopted. The advancement in the structural engineering field afforded by the biological approach relies in appreciation of operational complexities of biological systems, in general, and human locomotion, in particular. This allows fundamental understanding of pedestrian behaviour and its determinants in the presence of vibration applied by the walking surface to be gained with the ultimate goal of better characterisation of the self-excited forces exerted by the pedestrians, which are the main concern in structural engineering since they can drive structural instability. With all this in mind, a biomechanically-inspired inverted pendulum pedestrian model is explored in the context of forces generated on the supporting surface undergoing lateral or vertical motion. Consideration is given to the gait balance control mechanisms specific to these cases. It is shown that the net, destabilising or beneficial, self-excited forces can be generated without necessarily assuming synchronisation, but considering simple mechanics and control requirements of walking. Probabilistic stability criteria against lateral instability of structures under the action of crowds are then formulated and used in combination with the self-excited forces derived from the studied pedestrian model to show their applicability. The experimental setup is developed based on a laterallydriven instrumented treadmill. A motion capture system is utilised to obtain data on the kinematics of human gait and to facilitate an immersive virtual environment representative of a bridge, delivered through a head mounted display, and the treadmill belt control mechanism allowing for automatic adjustment of its speed to that of the walker. The results from the tests conducted on the setup give supporting evidence for applicability of the inverted pendulum pedestrian model and the foot placement balance control mechanism, also revealing influence of the visual environment on the selfexcited forces. Owing to the advances in experimental protocols and data processing, attractive patterns in pedestrian stepping behaviour on laterally-oscillating ground are identified and analysed in the context of structural stability. The premise underlying this thesis is that, despite the ubiquitous complexity of human behaviour, walking gait obeys a set of universal rules which are trackable and quantifiable. Uncovering these rules can help in defining more reliable models of pedestrian loading and structural response. Therefore, the research approach presented in this thesis departs from the approach found in the existing codified design guidelines, calibrated by top-down empirical models, and current modelling trends based on stochastic load description towards the bottom-up approach formulated on more deterministic treatment of the pedestrian loading.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available