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Viscous damper is a supplementary damping device which increase the damping ratio of structure and dissipates the energy of a seismic load. Supplementary damping systems can be categorized to active, semi-active and passive. General, passive damping devices may be classified as either displacement-dependent or motion-depended, or a combination thereof, and may be configured to act in either a linear or nonlinear. Damping device is a flexible structural element that dissipates energy due to relative motion of each end of the device. They include all the components required to connect damping devices to other elements of the structure and may have several geometrical configurations. 
In this dissertation is examined the appropriate design procedure of the distribution of fluid viscous dampers in the structure. It is considered a preliminary method to define the target damping ratio. Numerical seismic analysis is governed under a finite element software (SAP2000©), to determine the response of several plane and three-dimensional moment resisting frames. The beneficial of the installation of dampers is evaluated under structural analysis. The results compared from a maximum inter-storey drift and an energy point of view. The possibility of a better economical solution compared to traditional anti seismic techniques is also discussed. Finally, future requirements are proposed.

Ingénierie, informatique & technologie > Ingénierie civile

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The use of high strength materials and the development of computer methods allow engineers to design lighter and more slender footbridges. These structures are more and more flexible and often have one or more natural frequencies in the range of the loading frequencies due to human activity. Furthermore, the structural damping is often low, which make them sensitive to human-induced loading. The lateral force resulting from human walking may lead to large amplitude vibrations and one can observe an interaction (synchronization) between the pedestrians and the structure.

This work investigates the human-structure interaction. Firstly, a single mode model is studied modeling the pedestrian, with a Van der Pol oscillator. A multiple scale analysis shows that the response is governed by a dimensionless group, expressed as a function of the mass of the pedestrian, the modal mass and the structural damping. Afterwards, the influence of a second mode of vibrations is analyzed by adding an additional degree of freedom to the structure. The multiple scale analysis shows in this case that the response is governed by two dimensionless groups, expressed as a function of the mass of the pedestrian, the modal masses of the two considered modes, the structural damping and the frequency detuning between the two modes. Eventually, a case study is analyzed considering the Mantes-la-Jolie – Limay footbridge near Paris. L'utilisation de matériaux à haute performance et le développement des méthodes de calcul par ordinateur permettent aux ingénieurs de concevoir des passerelles de plus en plus légères et élancées. Ces structures sont de plus en plus flexibles et possèdent souvent une ou plusieurs fréquences propres dans le domaine des fréquences des sollicitations résultant l'activité humaine. De plus, l'amortissement structurel est souvent faible, ce qui les rend sensibles aux sollicitations induites par le passage de piétons. La force latérale engendrée par la marche de piétons peut conduire à des vibrations d'amplitude importante et l'on peut observer une interaction (synchronisation) entre les piétons et la structure. 

Ce travail investigue ce phénomène d'interaction piéton-structure. Un premier modèle considérant un seul mode est d'abord étudié, modélisant le piéton par un oscillateur de Van der Pol. Une analyse à échelles multiples permet de montrer que la réponse est gouvernée par un groupe adimensionnel, fonction de la masse du piéton, de la masse modale et de l'amortissement structurel. Par la suite, l'influence d'un second mode de vibration est étudiée en ajoutant un degré de liberté supplémentaire à la structure. L'analyse à échelles multiples démontre dans ce cas-ci que la réponse est gouvernée par deux groupes adimensionnels, fonction de la masse du piéton, des masses modales des deux modes considérées, de l'amortissement structurel mais également de la différence de fréquence entre les fréquences propres de chacun des modes. Finalement, une application sur une passerelle réelle est étudiée en considérant la passerelle de Mantes-la-Jolie - Limay en région parisienne.

Footbridge --- Synchronization --- Pedestrian --- Van der Pol oscillator --- Passerelle --- Synchronisation --- Piéton --- Oscillateur de Van der Pol --- Ingénierie, informatique & technologie > Ingénierie civile