The Studies On Damage Identification Method And Damage Results Visualization In Arch

Bridge is one of the vital parts of the traffic and transportation system. The healthy status of bridge structures is the premise for traffic and transportation system to operate normally. At present, some bridges appear aging, damage and crack even breaking down collapses for some reasons, such as design, construction, management, natural disasters and so on. There are too many examples to cite individually. Thereby, it is of great significance in theory and practice to perform health monitoring for bridge structures. Also, because monitoring results are rather abstract and difficult to be accepted, researchers are actively exploring how to show the monitoring data for a more intuitive description of the image.Structural damage identification techniques are the important components of health monitoring system of bridge structures. The vibration-based methods for the structural damage identification are the hot researches at home and abroad. Many theories and methods for damage identification have been presented, however, there are varying certain limitations in these techniques for damage detection to some degrees; Recently, wavelet analysis as a new kind of digital signal processing tools have the capacity of charactering the local features of signals in space and frequency domain, can make a good analysis of signal singularity, for this reason which can be widely applied in injury recognition area; At the same time, the application of visualization techniques in medicine, geology and other fields is more, but less in damage detection area. For the current research status of structural damage identification method and the needs of cutting-edge issues, in this thesis research is emphasized on damage identification of the arch structure, combined with wavelet analysis theory. The damage detection indexes of arch structure are formed and the injury recognition results are visualized vividly.The research works in this dissertation mainly include:(1) A general view of the latest development in the fields of damage detection and diagnose based on structural mode at home and aboard. The development and application in damage detection with wavelet analysis as powerful tool in irregular signal are illustrated. The technique and use of graph and image at present are summarized. The necessary and feasibility of realizing damage identification visualization are analysis.(2) The vibration characteristics of arch is heavily researched. The establishment and solution of vibration differential equation of intact and damage arch are analyzed, replacing damage with torsion spring, giving the structure of boundary conditions, and obtaining the natural frequencies and mode shapes. Simultaneously parabolic arch is analyzed.(3) Vibration characteristics in intact and damaged arch are simulated by the finite element method. Displacement modes and strain modes are simulated separately employing line elements and solid elements, two different boundary conditions (hinge support and fixed support) are used. The damage detection methods such as frequency perturbation method, mode difference, modal curvature difference, strain mode et al. are constructed based on the simulation.(4) The wavelet analysis theory is applied to the arch structure damage detection. The damage identification results via the continuous wavelet transform and multi-resolution analysis are studied; the relationship between the Lip index and damage singularity is analyzed and the extent of injury is determined through concentration factor. Simultaneity the damage identification for the multi-cracks arch and parabolic arch is discussed; the effects of wavelet vanishing moments, the boundary and noise on the damage identification are research.(5) Displacement mode test and strain mode experiment of the arch structure are performed, the input and output approaches on single-point excitation and multi-point response, multi-point excitation and single-point response are selected, acceleration sensors and strain gauge are used, a single crack and multi-crack are set up in arch, the mode frequencies and vibration shapes for damage identification in diverse conditions are studied.(6) The concept of visualization is introduced to the damage detection field, describing the application of visualization in other areas, the classification and comparison on visualization are studied, and the implementation method of the graphical visualization and image visualization are discussed, finally the arch structure damage identification results are visualized. The regularity of visual damage results is analyzed, and the following research on the visualization of the structural damage detection results is given. The main conclusions formed during the study are:(1) The vibration equation of arch is a 6 order differential equations, the characteristic equation of a single injury arch is the determinant of the 12 order square matrix; (2) The injury enable mode shape to exist singularity in damage position, resulting to the structural damage detection by mode variety, curvature mode change, and strain mode et al., and a more obvious detection results using wavelet transform; (3) The damage location and damage degree are two important factors affecting the damage detection, is a pair of mutual restraint combination. The small injury near mode nodes is not conducive to be identified; (4) the visualization of structure damage identification results show the appearance of the structure, meet the people's visual perception and is more easily accepted.The innovations of this paper are:(1) The selection and analysis of the typical structure:arch is a relatively complicated structure, circular arch and the parabolic arch is employed more in engineering, whereas there is the less research of damage detection in arch. In the paper, the vibration characteristics and the numerical simulation of the arch is studied, and the arch modal testes are carried out.(2) The impact of mode node to damage detection:there are more mode nodes (1mode node in first mode) in arch structure relative to mode nodes in the beam and plate. In this paper, the influence of mode nodes position and number in arch on the damage detection is investigated, the multi-mode damage identification approach is proposed, and the combination features of damage location and damage severity in structural damage detection is discussed.(3) The damage detection in arch with wavelet analysis:the wavelet analysis has a good recognition to the singular signals, the vibration shape in the damage arch is a discontinuous mode, which containing the singularity in damage location. The damage identification methods in arch are increased and the crack detection effect is improved by introducing wavelet analysis.(4) The integration of the visualization and damage detection methods:damage detection indicators such as the frequency variety, the vibration change, strain testing, and optimization algorithms, fitting for the part of the structure are formed during the years of development, wherever the application of the indicator to the engineer structure is restricted for the abstract of the damage indicator. In the paper, first, the outline information of arch is performed in visualizing, then damage index is converted into the corresponding gray and color, finally the structural image containing damage is displayed exactly and vividly.