Bridge Damage Identification Based On Optimal Wavelet Packet Decomposition Under Moving Loads

With the rapid development of China's economy,as the main hub of transportation,the bridge,bears more and more heavy traffic tasks,and its safety requirements are higher and higher.During the period of service,in order to quickly and effectively identify the damage location and extent of bridges,and take effective measures to ensure the safe operation of bridges,the bridge structure damage identification technology is applied more and more widely in the field of bridge engineering.Bridge structure damage identification technology plays a decisive role in protecting people's lives and property and national economic security.Therefore,it is necessary and important to study the damage identification technology of bridge structures.In identifying bridge damage,how to identify the location and degree of damage quickly and effectively has always been the focus of research.At the same time,the measured signals in practical engineering are often affected by environmental factors,so that the effective information is drowned by noise.Therefore,how to effectively reduce the noise in the measured signal has also become an important part of the research of bridge structure damage identification technology.(1)This paper introduces the background and purpose of this study,and expounds the research status of bridge structure damage identification technology.On this basis,the main research contents and research ideas of this paper are drawn.This paper expounds the theory of wavelet analysis,and points out that multi-resolution analysis can only subdivide the low frequency part of the signal.The theory of wavelet packet analysis is introduced,and the characteristics of the low frequency and high frequency parts of the signal can be subdivided simultaneously by wavelet packet analysis in signal processing are pointed out.Compared with multi-resolution analysis,the timefrequency resolution of the signal is greatly improved.(2)The concept of wavelet packet energy,the construction method of wavelet packet energy and the selection of optimal wavelet basis and decomposition level are described.Based on the energy of the wavelet packet,the energy denoising method of the optimal wavelet packet decomposition and the damage index-the total energy change rate index of the wavelet packet(DSI index)are proposed.(3)Taking the main bridge of Dayehu Bridge as the engineering background,the finite element model is established by using the finite element software midas,and the acceleration dynamic response of multiple nodes under moving loads under multiple working conditions is obtained.Based on the accelerated dynamic response,the optimal wavelet packet basis and decomposition level are selected according to Shannon entropy criterion.(4)By using the software of matlab and adding different intensity of white Gaussian noise to the original signal,the vibration signal with noise is simulated.It is found that the noise signal mainly exists in the high frequency band and the energy is small in the vibration signal.The simulation analysis of analog signals proves the effectiveness and robustness of the energy denoising method based on optimal wavelet packet decomposition in vibration signal denoising.Finally,the method is compared with the threshold denoising method of wavelet packet,which further proves the superiority,flexibility and stability of the method.(5)Bridge structural damage is simulated by reducing element stiffness,and the damage conditions are divided into single damage conditions(with different damage degrees)and multiple damage conditions.Then,the total energy change rate index of wavelet packet(DSI index)and the sum index of energy ratio of each frequency band of wavelet packet(DDI index)by others are used to identify the damage condition,and the sensitivity of the two indexes is analyzed in detail.The results show that the total energy change rate index of wavelet packet(DSI index)can effectively identify single damage condition and multiple damage condition,and the recognition effect is better than the sum index of energy ratio of each frequency band of wavelet packet(DDI index).(6)Based on the finite element model of the main bridge of Dayehu Bridge,20 dB,30 dB and 40 dB Gauss white noise are added to the nodal response of each damage condition,and the robustness of DSI index is analyzed in detail.The results show that the total energy change rate index of wavelet packet(DSI index)has better noise robustness.(7)Considering the effect of high-intensity noise on damage identification,the optimal wavelet packet decomposition energy denoising method is used to denoise the acceleration dynamic response of nodes under different damage conditions with 20 dB Gauss white noise.It is found that the denoising method based on the optimal wavelet packet decomposition energy method can effectively improve the accuracy of the total energy change rate index(DSI index)of wavelet packet in bridge damage identification.(8)The total energy ratio index(DSI index)of each node with different damage degree is processed by unilateral confidence interval.The relationship between DSI indices and damage degree of nodes near the damaged element after unilateral confidence treatment is simulated by cubic curve fitting.At the same time,the results of damage degree identification under the conditions of noise-free and 20 dB noise are analyzed.It is found that the damage index value of DSI can accurately identify the damage degree under the condition of noise-free,and can effectively identify the damage degree under the condition of noise.Finally,the main research contents of this paper are summarized,and the parts that still need further study are prospected.