Research On Development Of Cable Force Test System Based On LabVIEW Workbench

As the economical and efficient tension member, the cables are frequently applied to the modern structures due to their flexible laying pattern. The cables, working as the "lifeline" in the structures, tend to be influenced by external environment changes directly, leading to various kinds of defects, and resulting in partial or even whole structure. Therefore, whether the cables are asked for the construction control or condition assessment in the cable-supported structures* health monitoring, the study about testing cable force based on vibration method is valued in practice. Currently, the virbration test is almost the only choice in cable force measurement due to its mature theoretical basis and convenient repeatable procedures. Based on this test method, this dissentation had researchen on the subject of cable tesion test system. The main content is as followed:The cables' mechanical properties are irrestigated by analytical and numerical methods respectively based on the theory of the virbration method. According to the analytical method, a straight beam model considering bending stiffness and small sag cable model for dynamic analysis are introduced, and the corresponding frequency equations with the ideal boundary conditions can be obtained. But the actual cable's characters (geometric nonliearity) are in contradictions with the applicable condition and solving efficiency of analytical method, so the numerical method by beam element was conducted to analysize the parameters of the cables with given conditions. However, the conventional beam element is not able to simulate the bending stiffness in beam's section, therefore, it turn to the degenerated beam element to simulate the cables, and the results agree well with the results based on beam element and formula calculations. So it could be introduced into the cable force test system as a kind of cables' dynamic analysis mode, especially for some variable-section cables or for whose irregular material distribution and some cables under variable forces in space. The complete cable tension test system is developed based on the serials of NI instruments and the LabVIEW platform, to be operating in a computer-controled mode in test process. The eventual system is mainly formed by signals acquisition and conditioning module with human-computer interaction, data analysis files with test program's calling and savings modules. The Numerical verification and field testing are regimed to check the organized measurement system. For the former, the time domain signals picking up by the accelerometers are simulated via the time-history analysis of numerical models under single-pointed random loadings or single-pointed harmonic loadings or multi-pointed Gaussian loadings with various different sampling times. Then by way of comparing this test system's results with the pre-definited tension set in numerical models according to conditions as above-mentioned, it could verify the accuracy and general application. The discrepancy between the results is lower than 5% just satisfying the error limit in the engineering application. For the latter, the total and finial assembled system is operated to verify the effects of this composing hardware and software, with difference 7 %.