Research On Online Safety Assement Method Of Cable-stayed Bridges Based On Health Monitoring

Long-span bridges’ safety assessment is one of the aims of structure health monitoring,whose importance has been widely confirmed.In order to grasp safety condition of bridges in real time,it is urgent to achieve the real-time identification of the static and dynamic characteristics of the bridge structure,the automated updating of the finite element model and the on-line safety assessment.Taking Guanhe Bridge as the engineering background,an on-line safety assessment method of long-span cable-stayed bridges based on the health monitoring is attempted.The main research works are as follows:(1)The frequency-MPD stabilization diagram is generated by the data-driven stochastic subspace identification method,which is automatically analyzed via clustering analysis,thus the automated identification of modal parameters is achieved.Thus the automated modal parameters identification under the ambient vibration is achieved.(2)The influences of environment effects at different time scales are analyzed statistically,and the polynomial model between operating environment effects and modal frequencies is established.(3)The response surface model updating method based on Bayesian framework is derived,and SGD optimization algorithm and Adam optimization algorithm are introduced to solve the parameters.And automated model updating method of cable-stayed bridge is established by combining automated modal parameters identification method.(4)The typical structural responses of cable-stayed bridges,such as modal frequency,strain and cable force,are selected as the indicators of safety assessment.The weights of the three indicators are assigned by combination of precedence graph method,entropy method and game theory.And the online safety assesment method of cablestayed bridges is established by combinening automated modal parameters identification and automated model updating.The main conclusions are as follows:(1)Numerical examples and real bridge analysis indicate that the method can be used in the case of less prior information,and automatically identify modal parameters of close modes structure that shows good frequency identification accuracy.(2)The results of statistical analysis indicate that the modal frequency of the cable-stayed bridge decreases with the increase of temperature and vehicle load.The polynomial model including the average temperature of the section,the vertical acceleration RMS and other factors is able to accurately describe the relation between the modal frequency and the operating environment effects,and can be used for the subsequent on-line safety assessment of the cable-stayed bridge.(3)The results of automated model updating of Guanhe Bridge indicate that the effect of automated model updating method is moderate good as the maximum relative error of the calculated frequency after updating is within 5%,providing a benchmark finite element model for on-line safety assessment of cable-stayed bridge.(4)The on-line safety assessment of Guanhe bridge based on the monitoring data in a period of time is carried out,and the comprehensive safety score is stable at about 84 points,indicating that the safety condition of Guanhe bridge is maintained at a good level.