Research On Safety Early Warning Index Of A Bridge Health Monitoring System

How to accurately and efficiently obtain the finite element model which is closer to the actual engineering structure and scientifically and reasonably realize bridge safety early warning are the research hotspots at home and abroad.Taking a cable-stayed bridge health monitoring system as the research background,this paper systematically carries out the application research of bridge structure model updating and safety early warning based on real-time monitoring data by using response surface method combined with model-based early warning and model-free early warning.The specific contents and main research results are as follows:(1)Taking a cable-stayed bridge as an example,the health monitoring system of the cable-stayed bridge is designed according to the overall design principle of the bridge health monitoring system and the selection principle of sensor layout.Based on the vibration acceleration monitoring data,the stochastic subspace identification is used to identify the modal parameters,and the peak picking method is used to remove the false modes.The identification frequency is in line with the estimated results of the specification,which verifies the effectiveness of the stochastic subspace method in the modal parameters identification of bridge health monitoring.(2)According to the bridge design data,the initial finite element model was established.The objective function is constructed based on the dynamic data of the first four order vertical frequencies and static data of the cable force under dead load.The third-order response surface method is used to fit the modified objective response surface functions,and the fmincon function is used to optimize the modified results.The error between the corrected results and the measured results is less than 4%.By comparing with the correction results of the statics and the dynamics,the comparison shows that the combined static and dynamic correction using the third-order response surface can obtain the finite element model which is more close to the actual engineering response.(3)Based on the analysis of the strong correlation between strain monitoring data and temperature,a dynamic early warning threshold method of strain is proposed.The temperature strain in historical strain is stripped by EMD method.The linear relationship between temperature strain and temperature is obtained by combining the temperature fitting of measuring points.The subsequent temperature strain is calculated according to the fitting relationship,and the calculated temperature strain is used as the threshold calculation instead of the average value of monitoring data.The dynamic early warning threshold of strain is obtained by parameters.The yellow and red two-level safety warning system for bridges is established.The yellow warning threshold is based on the measured data of the bridge health monitoring system,and the red warning threshold is calculated according to the most disadvantageous loading of the modified finite element model.Applying the established safety early warning system to the actual bridge monitoring,the data histogram of each monitoring project shows that only a few data exceed the Yellow early warning threshold,and quickly return to the normal range,and no monitoring data exceed the red early warning threshold.It can be seen that the recent operation status of the bridge has not changed greatly and is in the normal operation state.(4)According to the bridge benchmark finite element model to simulate mid-span damage,the sensitivity of damage early warning indicators DSF and DSF' is analyzed.The results show that the damage index has strong stability and sensitivity to damage,and can be applied to damage early warning.Three days with large difference in the average temperature of the whole day were selected as three samples to analyze the characteristics of DSF and DSF' affected by temperature.The results show that DSF' has strong anti-interference ability.The early warning method based on the damage index DSF' is applied to real bridge monitoring.The damage index DSF' of bridge acceleration date under normal operation state is taken as the health sample set,compared the data sample to be detected and analyzed samples difference.The results shows there was no significant difference between two sample sets,which proves that the bridge is in good operation state.