Keywords: dynamics, bridge, human gait, multibody system, vibration, interaction, moving load, contact force.

Modern pedestrian bridges are very often light-weight and flexible structures, where the first natural frequencies of vibration may fall close to the dominant frequencies of the dynamic excitation due to walking or running. Such bridges are susceptible to vertical as well as to horizontal vibrations leading to a resonant response characterized by high levels of vibration and hence a dynamic design is necessary. Although such vibrations generally do not cause usually structural problems, they can induce some uncomfortable sensation, and so some codes or standards establish maximum acceptable values of acceleration, normally expressed as a function of the fundamental frequency of the bridge. The improved design of elastic bridges must take into account the phenomena of the man-bridge interaction and its vibration perception by human beings.

The paper deals with the investigation of the dynamic interaction between human gait and the elastic bridge for the prediction of bridge response and human body vibration. First the difference between the response of the bridge loaded by the contact force, representing a walking person, which was fixed in position and by the force moving in time has been demonstrated. The developed time and position dependent model for walking persons gives realistic results for different simulations.

Then a suitable model of interaction between human gait and elastic bridge has been developed [1]. The model includes the biomechanical multibody model of the human being, its feedforward-feedback control of the human gait, the finite element model of an elastic bridge and the interaction between the biomechanical model and the bridge. The mutual interaction is modelled by contact force influence using the concept of co-simulation. Several real elastic bridges have been investigated. The model enables the investigation of many different phenomena starting with different human gaits, different stabilizing feedback laws and ending with the influence of bridge design (given by stiffness and damping values) on the human perception. The mutual influence seems to be a complex phenomenon.

The proposed models based on the contact force or on the co-simulation of pedestrian-footbridge systems can be used in practical design of bridges in all situations when the dynamic response from moving people can be significant. The dynamic loading is defined more precisely in comparison with traditional methods (e.g. fixed-position pedestrian load-time function analysis).

1

M. Valášek, T. Vampola, J. Máca, "Investigation of Interaction of Human Gait and Elastic Bridge", in M. Papadrakakis, N.D. Lagaros, M. Fragiadakis, (Editors), "COMPDYN 2009, Computational Methods in Structural Dynamics and Earthquake Engineering", Rhodes, Greece, 1-12, 2009.

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