Dynamic Behaviours And Damage Identification Of Frame Structures With Cracks

In engineering practice, most of structures work with cracks, and the presence of cracks will lead to the change of their dynamic behaviours. Therefore, it is important to study the dynamic behaviours of frame structures with cracks. Now, both analytical method and FEM are commonly used for the study in the literature. However, disadvantages are remained. The analytical method is only applicable for beams with cracks. When FEM are used, errors arise due to the model approximation. Moreover, the stiffness matrix becomes singular as the crack size tends to zero.In this thesis, the dynamic behaviours of structures with cracks are studied through finite element method, which uses dynamic stiffness matrix. A new beam element with a crack is proposed, and its dynamic stiffness matrix is derived with the line-spring model of fracture mechanics. Numerical results show that this element is well applicable for the analysis of a frame with multiple cracks, and good accuracy is achieved. The effects of crack location, severity of cracks and multiple cracks on the dynamic behaviours are also analyzed.Then, damage identification is discussed. A new method——patch-test method is proposed and used toidentify whether cracks have occurred. Further, Genetic Algorithms are used to identify the location and severity of cracks. Numerical examples show that the above methods can achieve good results.