Applied Research On Cable Tension Monitoring Based On Frequency Method

Frequency method is widely applied in cable structural construction controlling and healthy monitoring for its relatively mature theory, easy operation and high precision. The accuracy of frequency method measuring cable force mainly relys on two aspects:one is the accuracy of cable frequency measurement, the other is the accuracy of cable force analysis and calculation. The former are mainly embodied on frequency identification, affected by field factor and signal processing method; the latter is primarily related to the selected calculation model, affected by cable stiffness, sag, boundary conditions and other factors. For different measuring components, the range of sampling frequency is varying at data acquisition, it needs accordingly adjustment. In the latter cable force analysis and calculation, cable boundary conditions are generally considered as consolidation or articulation, but the actual cable boundary conditions are not strict consolidation or articulation, over-simplification of boundary conditions will bring comparatively large errors, especially for short cables, the effect of boundary conditions can not be ignored.For the above questions, in order to improve the accuracy of cable force measurement, this paper makes the cable force monitoring of a practical bridge as background, mainly does some work as following:1) Introduced the theory of frequency method for measuring cable force, summarized y cabel’s static analysis theory and dynamic analysis methods, dynamic analysis methods include analytical method and finite element method, the accuracy of cable force calculation is related to cable stiffness, sag, boundary conditions and other factors,and analyzed the effect of several parameters for cable force measurement by frequency method, provided reference and basis for subsequent analysis and calculation;2) Elaborated the solving method for elastic restraint coefficient of cable boundary, use finite element software to establish cable model with considering elastic supporting boundary, made the cable force monitoring of a practical bridge as background, apply finite element numerical fitting algorithm to get a relatively high accurate value of cable force. Made an error analysis caused by wrong order frequency, the results showed that it will bring great cable force error, and thus introduced the method to determine the order of frequency;3) Analyze the reason of frequency measuring error and its effect for cable force measurement, obtained the relationship between cable force error and sampling frequency and sampling time. Combined with engineering background, elaborated the range of sampling frequency during frequency measurement.