The Studies On Structural Damage Identification Method Based On Edge Operator

Monitoring the condition and performance of vital structures is an essential issue in mechanical, civil and aerospace structures to ensure the service quality of structures and avoid grave accident. The structural damage identification technique is the fundamental technique of the structural health monitoring. Therefore, the researches are of great theoretical significance and practical value.By far, vibration-based damage identification technique has been the most widely used damage identification technique. The attractiveness of the technique is that it has no requirement that the structure under performance taken out of service for inspection and an automated continuous monitoring system can be developed because of its simplicity, minimum interaction with users. According to whether or not the feature extraction demands the structural mathematic model (generally FEM model), the vibration-based technique can be divided into two categories, namely the model-dependent method and the model-free method. The model-dependent method has to establish the accurate mathematical model of the structure, which would be quite challenging in case of large-scale structures. Instead, the model-free method has no requirement to establish the mathematical model of the structure. It solely relies on structural responses, which is available for practical implementation. For the improvement and perfection of the model-free method, with the support of the project (serial number 20023) entitled'Research and Development of Health Monitoring System for Long Span Bridge'which is provided by The Department of Communication of Hunan Province, further studies are addressed in this dissertation.According to the analogy between structural damage identification and edge detection in digital image, a new method based on edge operator is developed.As damage occurs, the changes of dynamic characteristic at the damaged place should be different from that of the undamaged place. The damaged place is similar to an edge point compared with the undamaged place. Inspired by those, the edge operator is introduced for damage location. In this method, first the wavelet packet energy square ratio—the ratio of the energy square sum of signal component decomposed by wavelet package before damage to the square sum after damage—of every node is obtained, then the edge amplitude is computed with an edge operator. Last the damaged place is judged according to the maximum of the edge amplitude. For demonstration, the numerical studies under different loads on many models, i.e. a simple beam, a rectangular plate and a plane frame are performed, the analysis result the method can not only accurately identifies the structural damage, but also operates simply , and have broad application prospects.