Studies On Non-Destructive Damage Detection Of Bridges Based On Linear And Nonlinear Dynamic Characteristics

In this thesis, damage detection techniques developed by specialists and scholars are categorized and compared from viewpoint of mechanics and mathematics, then the main tasks, i.e. the experimental studies and theoretical analyses about structural damage detection are carried out based on structural nonlinear dynamic characteristics.The research objectives of damage detection in this thesis are urban reinforced concrete and prestressed concrete bridges. Two approaches, i.e. finite element numerical value simulation and tests are developed in this thesis.Numerical value simulations studies are mainly used for single degree of freedom(SDOF) structure and simply supported beam model whose damages are the occurrence and extension of the crack. Two statuses of the cracks are assumed under dynamic loading: completely open and completely closed during structural vibration. The structural cracked zone can be simulated by nonlinear element whose stiffness is relative small when the cracks are open and equals to structural virgin stiffness before cracking when the cracks are closed during structural oscillation. Under these assumptions, three kinds of excitations, namely, harmonic force with frequency equal to the structural fundamental frequency, harmonic force with frequency equal to half of the structural fundamental frequency and pulse force are inputted to the undamaged and damaged structures. Then under the same excitation, the undamaged structural displacement responses, velocity responses, acceleration responses, jerk responses and responses of integrated displacement are compared with that of the damaged ones. The compared results indicated that the structural integration of displacement responses is most sensitive to structural damage assumed in this thesis. Hence, for such kind of damage, using the new damage indicator, namely, displacement integration, to identify structural damage should be paid more attention.In aspect of numerical simulations studies, four force-displacement curves of SDOF structure are designed to simulate undamaged and three different degrees damage models. Three kinds of excitations, namely, harmonic force with frequency equal to the structural fundamental frequency, harmonic force with frequency equal to half of the structural fundamental frequency and pulse force are applied to such four kinds of models. The displacement responses of the four kinds of models are calculated using SAP2000 and the integrations of displacement responses are obtained by numerical calculations. Then, the integrations of displacement responses of the four kinds of models are compared under each kind of excitation. The comparison results indicated that the structural integrations of displacements responses decline with structural damage degrees'increasing under all the three kinds of excitations. Also the quantity relationship between integrations of displacement responses and damaged degrees are...