ZFFT-based Bridge Cable Force Measurement And Application Software Development

The safety and reliability of large bridges are of great influence to the society, and the stress state of the cable is one of the important indexes to evaluate the safety of the bridge. The cable force measurement method mainly has the oil pressure gauge method, the compression stress method and the frequency method. The hydraulic pressure gauge and the compressive stress method are only suitable for the detection of the cable force of the bridge. However, the frequency method has the equipment can be reused, the whole set of equipment to carry, easy to install and so on, it is almost the only choice when the cable force of the large bridge has been completed. In engineering, the measurement accuracy of the cable force is less than ±6%, and the precision of the cable force measurement of the frequency method is difficult to meet the requirements of engineering application. Therefore, it is necessary to do further research on improving the accuracy of cable force measurement. In view of the frequency method to measure the cable force, the research of the vibration signal processing method is helpful to improve the detection scheme and improve the accuracy of the detection results. Specific contents and results are as follows:(1) Butterworth filter, Chebyshev filter and Wavelet three methods of cable vibration signal noise reduction are compared. Wavelet noise reduction processing of cable vibration signal, spectral curve around the peak frequency value corresponding to the location of the premises is most easily determined. Mechanism of wavelet coefficients and noise signals with different properties at different scales according to the rules established accordingly. In the wavelet domain using modulus maxima method of wavelet coefficients cable vibration signal processing with noise, the wavelet coefficients after processed to reconstruct the original signal, and then get the closest estimate of the true signal. Wavelet denoising method of Cable Vibration Signal Denoise effect is better than that of Chebyshev filter and Butterworth filter, using the modulus maxima method in different scales of cable vibration signal processing, to improve the anti-interference ability of the cable vibration signal.(2) The application of ZFFT method in the processing of cable vibration signal is studied. The low-frequency cable is very low, often with bridge deck and pylon of the fundamental frequency coupling, resulting in measured cable vibration signal processing results in spectral curve often appear frequency aliasing phenomenon. The spectrum thinning technique based on ZFFT algorithm is applied to the case of the dense frequency components of the serious interference phenomenon. Therefore, the ZFFT algorithm is applied to the identification of the vibration frequency of the bridge cable. The ZFFT algorithm is used to analyze the vibration signal of the cable, which has the characteristics of spectrum analysis in the selected frequency range. It is helpful to improve the frequency resolution and reduce the number of sampling points. Measured cable vibration signal of ZFFT analysis of the experimental results show that, in the sampling length and sampling rate parameters of the same case, ZFFT analysis obtained the frequency resolution than the traditional Fourier analysis method is 100 times higher, which in a certain extent improve the cable force measurement accuracy.(3)According to the actual application requirements of cable force measurement, the design of system hardware circuit and the development of application software are realized. By LabVIEW programming application, follow the modular design concept. The main function modules include real-time display of the sampling signal, automatic recognition of the fundamental frequency of the cable, automatic generation of the detection results, and the quality evaluation of the data analysis processing and the detection object. The design of hardware circuit mainly includes signal amplifier, filter circuit module design, the realization of STM32 microcontroller minimum system and the software programming of data acquisition unit. Finally, the cable force measurement system on-site test results with the bridge in the 13-year target of cable force adjustment compared to obtain the maximum error is less than ± 3%, explained reliable measurement results and Cable force measuring system meets the requirements of engineering applications.In this paper, the ZFFT method is applied to the measurement of bridge cable force, help to improve the detection accuracy of cable force, it has some practical significance and broad application prospects.