Research On Cable Tension Measurement Of Cable Supported Structure Based On Improved Frequency Method

String structure is widely used in all kinds of long-span space structures as a space structure system with uniform force and convenient and reliable construction.As an important flexible component of string structure,cable bears large prestressing force.Measuring the cable force is of great significance for evaluating the health status of inservice projects.Frequency method has become the most commonly used method for cable force measurement in engineering due to its advantages of high accuracy and simple operation.The existing method of measuring cable force by frequency is suitable for long-diameter cables.Most of the cables in the string structure are short and thick.The bending stiffness and boundary conditions of the cables have great influence on the results of cable force measurement.Therefore,based on the idea of calibration,this paper proposes an improved method of frequency measurement of cable force,and presents a finite element simulation method for testing cable force based on LS-DYNA software.The main research contents are as follows:(1)Based on the calibration idea,an improved frequency method is proposed in this paper.In this method,the exact database of cable force and frequency is obtained through the tension stage of the construction of short and thick cables,and the functional relationship between cable force and frequency is fitted.The cable force is obtained by measuring the frequency of the cable during service,which provides a basis for the health assessment of the in-service string structure.(2)In this paper,the database of cable tension and frequency is obtained through the tension tests of strands and semi-parallel wire bundles.Based on some data points,the function relationship between cable force and frequency is fitted,and the cable force errors of other data points are calculated by using the function relationship.The results show that the error between the actual cable force and the improved frequency method is 11%,and that of the existing frequency method is 64%.The improved frequency method has good applicability.(3)Based on LS-DYNA software,this paper presents a numerical simulation method to test the cable force.Firstly,an improved finite element model of cables is established,and the accuracy of the model is verified.The database of cable force and frequency is obtained by harmonic response analysis of cables.The results show that the error of the improved frequency method is 11%,and that of the existing frequency method is 87%.The improved frequency method is superior to the traditional frequency method.(4)The database of cable forces and frequencies obtained from the test and finite element simulation of cable forces of plane beam string and suspended dome is presented.The improved frequency method and the existing frequency method cable force formula are used to calculate the cable force.The error of the improved frequency method cable force is 9%,and the error of the existing frequency method cable force is 40%.Through the cable force analysis of two-way beam string and truss string in service,the same error of the improved frequency method in calculating cable force is far less than that of the traditional frequency method,which verifies the accuracy of the improved frequency method based on the calibration idea.