Study on Test Method of Cable Force of Stay Cables of Large Bridge Based on Zoom-FFT Algorithm

Abstract

The cable-stayed bridge is often influenced by the external environment (corrosion and vibration fatigue) during operation, which reduces the strength of stay cables and makes it fatigue, and it shortens the life of a cable which destroys the structural performance. Therefore, cable force measurement of stay cables is of great significance for cable-stayed bridge in both construction period and completed status. The measurement of the fundamental frequency of cable vibration is one of the key problems in cable force measurement. The author puts forward Zoom-FFT method which can obtain the fundamental frequency of cable vibration with a high degree of accuracy. The general procedure for the determination of the fundamental frequency of stay cables is: (1) Cable-stayed vibration signal test was subject to spectral analysis, and then read each frequency value corresponding to the peak in the spectrogram, by making the subtraction between adjacent peaks in cable-stayed averaging method to obtain an approximate fundamental frequency value. (2) Read frequency value corresponding to the maximum peak in the spectrogram, calculate the corresponding order, and obtain an approximate fundamental frequency value again. (3) According Zoom-FFT algorithm, make a detailed analysis in the range of selected bands, and determine the frequency value corresponding to the highest peak value, which is the fundamental frequency. (4) Bring the fundamental frequency values into the string vibration equation, and then determine the cable force. The proposed method improves the accuracy of recognition of fundamental frequency of stay cables, and greatly reduces the technical problems in cable force testing, which can be widely applied in cable tension detection in industry field.