Structural Damage Identification And Numerical Simulation

In the fields of civil, mechanical and aerospace engineering, structural damages such as cracking and aging etc. to some degree during the structures' service life occur from time to time. Some invisible damages do not alert the engineers in time and may result in disastrous consequences and ultimately cause substantial loss of life and property. Therefore, it is important to monitor structures and to detect damages at the earliest possible stage.Sponsored by the National Natural Science Funds of China, this research focused on identification of the damages or defects in engineering structures. The main contents and contributions of the research are summarized here.An approach of structural damage identification based on the element's modal energy was discussed. A sub-modal strain energy method was proposed according to the discussion to identify damage location in space frame structures.The application of Artificial Neural Networks (ANN) and Genetic Algorithm (GA) in structural damage detection was investigated. The procedure of identifying damage can be defined as a minimization problem. The optimum solution can be obtained effectively by using GA. Since GA usually needs a long calculating time in use with the Finite Element Method (FEM), a method combining matrix perturbation with GA was brought forward which works well with the simulations. In addition, a damage detection technique combining ANN with GA was proposed so that serious damages in a structure can be identified.A new method, called flexibility curvature method, to localize the damage in structures was presented. The method is not only highly-sensitive to damage, but also able to identify the damage location in structures without baseline modal parameters. Furthermore, the method has advantages of involving a small quantity of calculation and being simple and easy in use. The damage in structures can be detected with satisfactory precision by using only a few lower modes.Damage identification using only a few testing points information was discussed by using flexibility curvature method and curvature mode shapes method. With the limited number of degree-of-freedom measurement information, it is difficult to locate structural damages with flexibility curvature and curvature mode shapes but it is effective to locate the damages based on the difference between the curvature mode shapes and the difference between the flexibility curvature for theintact and the damaged structure.The influence of measurement error on the identification results was discussed. The computational example indicates that it is impossible to identify the damaged zone even though the measurement error in the displacement mode shapes is 1%, if curvature modes and flexibility curvature are obtained from the displacement mode shapes and used to locate the damaged region.A method was presented which uses test frequency data and element's modal strain energy combined with GA for identification of multiple damaged locations in a structure. It was also discussed how to locate multiple damaged zones in structures using curvature mode shapes and flexibility curvature.The absolute sensitivity coefficients and relative sensitivity coefficients of the modal parameters including natural frequencies, displacement mode shapes and modal flexibility were analyzed with respect to the changes in stiffness. Theoretical analysis and numerical simulation show that the sensitivity of the modal parameters to damage is related to the structural characteristics. For absolute sensitivity and relative sensitivity, none of the three modal parameters is dominant absolutely without precondition. This conclusion corrects the point of view that the modal flexibility is more sensitive to damage than either natural frequencies or the mode shapes.The influence of modeling errors on structural damage identification was studied. The effectiveness of damage location with modeling errors changes from case to case. Therefore the analytical model with error should be modified before it is used to identi...