Modal Parameter Identification for Transmission Tower Based on Point Spectrum Correlation Function of Time-Frequency Distribution

Modal parameter identification is the foundation of structure model correction, damage diagnosis and safety evaluation of the transmission tower. To obtain modal parameter identification method with clear physical meaning and practicability for transmission towers, the point spectrum correlation function of time-frequency distribution was used to deduce analytic expression of damped free vibration response of the structure. The deduction in this paper reveals the response function relationship between point spectrum correlation function values and structural modal parameters, and then the square root value of point spectrum correlation function is proposed to identify modal shape of the transmission tower. This method does not need time domain or frequency domain information from external excitation. Numerical example of transmission tower structure results show that the modal frequencies can be accurately achieved by spectrum and time-frequency analysis of vibration response signal. The maximum identification error of the first order modal shape of the structure is 0.54%, and the maximum identification error of second order modal shape is 1.52% using square root value of time-frequency spectrum correlation function. The structure modal frequency identification is not affected under the noise level of 10%, the maximum identification error of first order modal shape is 2.53%, and the maximum identification error of second order modal shape is 4.55%.