Study On The Structural Health Monitoring Of Nanjing Yangtze River Bridge And Its Key Technologies

The structural health monitoring (SHM) of a large bridge is an active research field of the bridge engineering. This is a very difficult task, which involves different subjects, and there is no more experience for reference because the study on this field in the word is still at the exploring phase. Firstly, state-of-arts of structural health monitoring is comprehensively reviewed. Then, taking the Nanjing Yangtze river bridge (NYRB) as engineering background, some key techniques about SHM for a railway bridge are investigated in this dissertation. The main contents are as following:(1) As an important part of this dissertation, the first SHM system for existing both highway and railway bridge has been built successfully in our country. The built system, which has the comprehensive monitoring contents and reliable monitoring means, is an advanced SHM system. Many difficult problems about the establishment of SHM system have been solved. Main software based on the Visual Basic platform and the real-time signal analysis program based on MATLAB platform are independently designed. At present, this system is working normally.(2) Signal analysis is a key technique for SHM. By using wavelet transform, the monitoring signals of bridge SHM are described on different scales. According to Lipschitz index, the principle of wavelet anti-noise is introduced, and noise elimination of the real-time monitoring signal is realized. At the same time, the eigenvector of monitoring signal energy obtained by wavelet packets can offer us the scientific basis for evaluating the structural state in both time domain and frequency domain.(3) Taking all the vibration monitoring signals of the bridge carrying both highway and railway traffic as non-stationary signals is firstly proposed. Combined the Hilbert-Huang transform (HHT)with random decrement technique (RDT), a new method of structural modal parameter identification in which the structural modal parameters of NYRB are identified is presented.(4) Based on the physical meaning of sensitivity and the existing finite element (FE) program, a simple and applied new method of model updating is proposed. In this method, the structural model is updated by modifying the parameters of design, and validated by structural natural vibration characteristics as well as stress-time response of the main members of NYRB. The FE model of NYRB built by ANSYS is updated by using the SHM signals, and the FE "baseline" model reflecting the structural current state is obtained.(5) The fatigue performance of railway riveted steel bridge is discussed in detail. According to the reliability theory, a limit-state function of fatigue failure for the S-N curve and Linear-elastic Fracture Mechanics (LEFM) methods are deduced, and the different random variables involved in the limit-state equation are discussed respectively. Using the advanced first-order second-moment (ASM) and Monte Carlo methods, the fatigue damage reliability and failure probability of the main members of NYRB are calculated. The results indicate that the fatigue failure probability of the NYRB main members is very small for its low live-load stress level.