Study On The Uncertainty Of Cable Structure Parameter Identification

As one of the main stress components of cable-stayed bridge,it is an important prerequisite to accurately identify the cable force value of cable and evaluate the measurement results scientifically to ensure the smooth construction and operation safety of cable-stayed bridge in the later stage.The accuracy of cable force test results by frequency method depends on the accuracy of model parameters and the reliability of the model itself.Based on the cable force measurement system initially established by the research group,this paper analyzes the relationship between cable force measurement and metrology,evaluates the uncertainty of different measurement models in the framework of uncertainty theory,and calibrates the dynamic measurement model of cable force with superior instruments to quantify it The uncertainty of the model itself.The finite element model of cable is established,and the comparison of different measurement models is carried out based on the evaluation results.On this basis,the field cable force test scheme is designed and implemented,the natural frequency of cable is extracted by spectrum analysis,the cable force value of the measurement model is calibrated by the pressure ring of the superior instrument,and the uncertainty of the cable force dynamic measurement model due to the dissatisfaction of the assumed conditions is determined.The main contents of this paper are as follows:(1)The current situation of cable force test,the theoretical method of measuring results evaluation in metrology and the method of cable parameter identification are investigated.This paper summarizes the common cable force testing methods and deduces the explicit expression process of the string model and the simple beam model in the frequency method.On this basis,from the perspective of metrology,it expounds the process of the analysis and processing of the measurement results from the error theory to the uncertainty theory,and analyzes the necessity and science of the cable force measurement results to meet the traceability of the measurement value,combing and analyzing The influence of cable length,cable density,bending stiffness and boundary conditions on the measured cable force and the identification method of each parameter in the cable force measurement model are discussed in the literature(2)Based on the uncertainty theory in metrology,this paper analyzes and sorts out the literatures about the uncertainty of measurement model in metrology,and completes the distinction between the uncertainty of cable dynamic measurement model in bridge engineering due to the unsatisfied assumptions and the uncertainty caused by the probability characteristics of parameters in dynamic measurement model.Combined with the actual case of short cable,the uncertainty of string theory model and simply supported beam model and the uncertainty caused by the probability characteristics of the parameters in the measurement model are obtained respectively.The iterative development process of cable force measurement model is analyzed.The probability distribution types of parameters and cable force output in the dynamic measurement model are determined by nonparametric hypothesis test theory,and the process of uncertainty caused by the probability characteristics of parameters analyzed by Monte Carlo method is improved.(3)Through the calibration of superior instruments to determine the uncertainty of the dynamic measurement model itself,the process of the cable force measurement results rising from the comparison between models to the calibration of the measurement model in metrology is completed.The finite element model of the cable is established to extract the natural vibration frequency of the cable,and different measurement models are brought into the Monte Carlo method to evaluate the uncertainty.Different measurement models are calibrated by reference value to determine the uncertainty generated by the measurement model itself.On this basis,combined with the measured data of the cable production site and the actual bridge,through the calibration of the superior instruments,respectively The probability characteristics of the model parameters and the uncertainty of the model itself are obtained.Then the uncertainty caused by the two factors is combined to get the final uncertainty of the measurement model.