Study On Theory And Application Of Damage Identification For P.C. Cable-stayed Bridge

Structural damage identification techniques are the important components of the health monitoring system of the bridges. The structural damage identification methods which based on the dynamic response of structures are very popular. The dissertation is devoted to break through the difficulty in the damage identification field on the basis of the existing methods.Firstly, a precise three-dimensional finite element model of a prestressed concrete cable-stayed bridge is established. Then the model is updated by a Jacobi parametric optimization method and the baseline FE model is obtained, which is more precise to describe the behavior of the cable-stayed bridge. Lastly, dynamic properties of the cable-stayed bridge are analyzed and the conclusion indicates that it has lower natural frequencies, dense modals and many coupled vibration.The sensitivity formulas of natural frequencies and mode shapes for different position in structure are derived based on the dynamic equilibrium equation of a free-vibration multiple-degree-of-freedom structural system. A three-dimensional finite element model of three-span continuous bridge is established and the sensitivity formulas are verified. In the end, the dissertation draws a conclusion that sensitivity of modal parameters for structure damage is different and the conclusion is also suitable for other beam-type structures.Based on the concept of modal curvature and flexibility matrix, two damage locating indices are constructed and the method which utilizes the local optimum rule to identify the damage is presented. Various damage cases simulated in the main girder are identified. The conclusions indicated that the damage locating indices can detect definitely the position and level of damage and it also has a better ability to resist the noise.Genetic algorithm (GA) is a novel global optimization algorithm appeared in recent years. When GA is applied to the damage identification field, it is necessary to regard the problem as an optimization one. A fitness function of GA is constructed with the flexibility rate of all measured points as the design variables. Various damage cases simulated in the main girder are identified. The conclusions indicated that GA can detect definitely the position and level of damage and it also has a better ability to resist the noise.Wavelet transform, a new mathematical manipulation, can obtain the best resolution both in frequencies domain and in time domain, which is the deficiency of the Fourier Analysis. The wavelet and its package decomposition in the damage alarm of bridges are researched. The signal in time domain decomposed by wavelet and its package can definitely identify the time of day when the damage occurred. So the purpose of damage alarm is reached, also the conclusion which high frequency signal is more sensitive to damage in the structures is verification through wavelet package decomposition.