Study On The Vertical Vibration Of Footbridge Considering The Interaction Between Human And Structure

When the structure meets the functional requirements,people's pursuit of aesthetics and space is getting higher and higher.As an important part of the city and scenic area,the footbridge has made rapid progress in recent years.But this kind of footbridge is usually lighter and the natural vibration frequency is relatively low,so it is easy to generate the human-footbridge resonance,causing the structure safety and comfort problems.For this kind of foootbridge,which has both walking and standing crowds,at the present stage,it only considers the incentive effect of walking group on footbridge,and does not consider the interaction between population and structure.And the theoretical and experimental studies in this area are also limited.In this paper,a light pedestrian bridge model is designed and produced in the laboratory environment.It is used to study the interaction between human and footbridge.It proves the necessity of considering the interaction between human and structure.On the basis of the existing research,three typical static human body models are selected,combined with a heavy footbridge model abroad and the light pedestrian bridge model designed and made by us.The dynamic characteristic and dynamic response analysis of the human-footbridge coupled system are carried out in consideration of human-structure interaction.The main summaries and conclusions are as follows:(1)Experimental study on the human-struction interaction.A fabricated steel structure-glass footbridge model is designed and built as a test platform.The rule of human-struction interaction is summarized and compared with the equivalent mass,and the result shows that: both the human body and the equivalent mass can reduce the first-order self-vibration frequency of the footbridge model,but the influence of the standing human on the footbridge model frequency is greater than the mass block.And the standing human can significantly improve the effective damping ratio of the footbridge model,while the same weight mass has no effect on the damping ratio of the footbridge model.Therefore,there is obvious error in the equivalent method of standing human equivalent to the same weight mass.In the calculation of dynamic characteristics and dynamic response of light structure,the interaction of human-structure should be considered.(2)Analysis of the influence of human-struction interaction on the dynamic characteristics of a footbridge.The results show that the forms of vibration equations based on three kinds of standing human body models are basically the same for different model.However,there were differences,such as the vibration mass and modal mass in the mass matrices,and the modal mass in the stiffness matrices and the damping matrices.The results of the three standing human body models coupled with the heavy and light two kinds of footbridge models are compared with the experimental values.It is proved that the three models have a certain reliability and wide applicability.The parameter analysis of the crowd-footbridge coupled system shows that the frequencies and damping ratios of the footbridge are more sensitive to the mass ratio and frequency ratio of human to footbridge,respectively.(3)Analysis of the influence of human-struction interaction on the dynamic response of a footbridge.The effects of three human models on the dynamic response of heavy and light footbridge are consistent.Analysis shows that: the dynamic response of footbridge is most sensitive to the frequency of human-footbridge coupled system,and the pedestrian frequency is closer to human-footbridge coupled,the greater the dynamic response of footbridge.In particular,when the stride frequency is equal or integer multiple to the frequency of the footbridge,the human-footbridge resonance will occur,and the peak response of a footbridge that the frequency in the range of the normal walking frequency of the pedestrian is far greater than that of the other bands.The resonance frequency is changed when the crowd is placed on the bridge,and the additional damping effect can reduce the response.Therefore,it is necessary to consider the influence of the crowds on the frequency and damping ratio of footbridge in order to ensure the accuracy of the calculation of the dynamic response.