Study On Modal Parameters Of Standing Human Body-structure Coupling System Exposed To Horizontal Vibration On Dynamic Characteristics

Human body model was considered as an additional mass attached to the structure surface for traditional structure design, but with the performance of the building materials continuous improved, the structure is becoming more slender, lightweight and even larger in cross-direction. There have been more and more accidents in coupling systems of human body and structure in recent years, the most typical accident is the London Millennium Bridge, when it is opened. The footbridge was caused excessive lateral vibration and forced to close due to a large number of pedestrians walking on it, after that, people had to spend a lot of money to repair. Structural vibration safety problems caused by pedestrian results from the beginning design, because human body was modeled as an additional mass and ignored the coupling of human body-structure. The interaction of the coupling system is more obvious especially for the structure with low natural frequency. Human body model simply modeled as an additional mass can’t have been able to satisfy the design requirements of modern structure. Therefore, an accurate and reasonable dynamic model of human body must be proposed, in order to meet the needs of modern structure design. The experimental results and theoretical analysis have shown that the human body is not a simple mass. Domestic and foreign scholars have proposed different simple human body model, but so far, there has not been any consistent international standard of dynamic parameters for human boy model.Up to now, the study of characteristics of coupling system has been mainly in vertical vibration field. For human body model, lots of different parametric dynamic model with different degrees of freedom have been proposed. However, there have been little studies for lateral vibration model of human body, and the related theoretical model is not yet accurate. It is still unknown that the vertical vibration model whether can be directly applied to the lateral vibration model for human body. Domestic and foreign researchers pay more and more attention to the interaction between human body and structure on lateral vibration, because of more and more accident for coupling system of human body-structure on lateral vibration. But unfortunately, an effective lateral vibrations human body dynamic model has not been proposed so far, because of complexity of human body and lack of a large number of experimental checking.In this paper, human body lateral vibraiton model, which was simplified as a model of bending vibration of beam, is proposed, referring the research result in the vertical vibration model of the human body. One end of the lateral vibration model is fixed, the other end is free. The coupling dynamic characteristics of human model with single degree of freedom and structure with single degree of freedom have been analyzed for different frequency ratios and mass ratios of the human body to the structure and different the damping ratios of human body in detail. Acceleration response spectrum of coupling system of human body-structure has been deduced. Lateral vibration platform was designed and made, at the same time, two order peak frequency of coupling system has been measured. The human body model is equivalent to a mass-spring-damper system with a single degree of freedom, and the frequency response function of coupling system was measured. The transfer function of the FRF has been fitted with least square methods, and the modal parameter has been identified based on the transfer function. In a simple two degree of freedom model as an example, analytical expressions of the modal parameters have been derived from the transfer functions of coupling system. The admittance circle has been fitted by least square methods, which can confirm multi modal dynamic characteristics of the coupling system.The innovation of this paper is to determine the parameters of lateral vibration for human body model with single degree of freedom. The model parameters of human body with single degree of freedom are generalized to the crowd model. It is very effective for slender and large span structure design with low nature frequency. According to the experimental study of human body-structure coupling system exposed to lateral vibration. The following main conclusions were concluded:(1) It is not just an additional mass system for human body exposed to lateral vibration, but a complex dynamic system;(2) The nature frequency of structure, that is the first-order modal of the coupling system, is not reduced significantly. On the contrary, there was second-order modal frequency for the coupling system of human body-structure in horizontal direction vibration. The response of FRF for the second-order modal is far smaller than that of the first-order modal, with large bandwidth;(3) It is not only a significant influence on the dynamic characteristics of the coupling system for the human body in different posture, but also affects the dynamic properties of the human body itself;(4) It is also a significant effect in amplitude for the model parameters of the coupling system, mainly affecting modal mass and stiffness;(5) There is a big difference between mode shapes of measured FRF and theoretical shapes of bending vibration of beam, mainly due to the people’s initiative caused by the vibration. People always keep themselves upright unconscious during the vibration, allowing the organization organs of the body in the best condition;(6) Human body is a very complex dynamic system with uneven distribution of damping. For different parts of the human body, the transmission functions are totally different. And the vibration attenuation is more and more serious from the bottom to the top.