Experimental Study On Time-varying Dynamic Characteristics And Fatigue Performance Of Crowd-structure Coupled System

In recent years,with the rapid development of tourism industry and the improvement of people’s aesthetic appreciation of structure,more and more light-weight,long-span and low-damping steel-glass composite pedestrian structures have emerged in large numbers.Such as Zhangjiajie glass footbridge,Linxia dadun gorge glass footbridge,Hebei baishi mountain glass walkway,Shanghai world financial center,etc.This kind of structure has the characteristics of light weight,low frequency and weak damping,and its dynamic characteristics are more easily affected by environmental factors and operating conditions,such as temperature,humidity,additional mass of static crowd,walking frequency of dynamic pedestrian,etc.At the same time,as the main load form on the footbridge and the main factor causing the human-induced vibration,people have the important characteristic of complex biological system.When interacting with the structure,the human-structure coupling dynamic system will be formed,including the static crowd-structure coupling dynamic system and the pedestrian-structure coupling dynamic system,which will have different degrees of influence on the dynamic characteristics of the structure,leading to large errors in the calculation of structural modal parameters.Modal parameters are the most commonly used dynamic parameters in the research and application of bridge vibration control,state detection,health assessment and vibration characteristic analysis of structural systems.At the same time,modal analysis can also evaluate the dynamic characteristics of existing structural systems.Not accurate modal parameters in the damage identification and model will lead to big error correction,even is wrong,so the modal parameters of the structure factor must be removed.In addition,under the action of crowd load,the pedestrian step frequency is close to the base frequency of the footbridge and it is easy to cause resonance,which leads to the problem of excessive vibration of the footbridge.When the vibration exceeds a certain range,it will cause cumulative fatigue damage to the footbridge members,affect the safety of the footbridge,and even cause the footbridge to collapse.Therefore,in the process of studying the above problems,the steel-glass composite pedestrian structure test platform was firstly built in the laboratory,and the dynamic characteristics of the structure under non-structural factors such as ambient temperature,additional mass of static population and dynamic pedestrian action were studied by field test method.Meanwhile,the fatigue life of the structure underexcessive vibration was estimated and controlled.The main contents of this paper include the following aspects:(1)Make the experimental model of footbridge structure.The finite element numerical model is established for modal analysis.The 941 B acceleration sensor was arranged on the test model,and the modal parameters such as frequency,damping and mode of vibration were obtained by using the experimental method.(2)Based on field experiments,the influence of ambient temperature on the modal parameters of steel-glass composite pedestrian structure was studied.Established the mathematical model between temperature and the structure modal parameters,gives the first three order vertical modal frequency of a linear fitting expressions of temperature change;(3)Experimental study on the influence of static population on dynamic parameters of footbridge.The 941 B acceleration sensor is arranged on the footbridge to measure the acceleration response of static pedestrians in different positions,different postures,different Numbers of people and other working conditions on the footbridge.The random subspace method is used for data processing to obtain the law of the influence of static crowds on the dynamic parameters of the footbridge.(4)Experimental study was conducted on the influence of vertical dynamic coupling effect of pedestrian structure on structural dynamic parameters and dynamic load factor of pedestrian load.Concluded that consider pedestrian footbridge-the vertical dynamic coupling effect,the change rule of the dynamic characteristics at the same time,this paper gives the rigid ground and flexible order 4 before the pedestrian bridge load dynamic load factor fitting formula;(5)Based on the crowd-structure coupling footbridge vibration fatigue performance evaluation: the use of stress and strain acquisition system acquisition,coupling vibration response of the structure of the crowd-get a pedestrian bridge dynamic stress-strain,the strain calendar for processing,get the fatigue stress spectrum.The deterministic s-n curve and Miner model were used to evaluate the fatigue damage and service life of footbridge,and the influence of related parameters on the fatigue damage and remaining life of footbridge was discussed.In addition,the vibration control of the structure was carried out,and the changes of the fatigue life of the structure under TMD control were analyzed.