Studies On Damage Identification Of Steel Member Structures Based On Vibration Test

With the quickly development of the societies and economy, the shape and function of the civil engineering structures become more and more complication, and the security of them is pained more attention to. More and more structural health monitoring(simplified in SHM) system are installed on the long-span bridge,large-scale space civil engineering, however, the key technique of the SHM system—damage identification has never been ultimately resolve, and it restricts the application and developing of SHM seriously.The structures damage identification based on vibration test was researched and developed widely, lots of methods were presented in past several decades, most of these methods can get a good results in the numerical analysis or in the experiment in laboratory. However, because the volume of the civil engineering is very huge, and the shapes are more complicated, observation means are restrict, and so on, the prerequisite test information of these methods are generally hard to get completely, the successful examples of damage identification and SHM of civil engineering structures are rare. The damage identification of civil engineering structures go to practical, there are a lot of problems need to be solved, most important of all, is to solve the parameter identification and damage identification in incomplete of the test information and the disturbing of test noise. In such background, two different methods of structures damage identification on steel member structures were presented in this dissertation, they are intelligent method based on genetic algorithm(simplified in GA) and analysis method based on residual force vector separately. In some examples of benchmark structure with the same test condition, the identification results were compared. This dissertation includes six chapters as follows:In the first chapter, the background of this dissertation are introduced firstly, Secondly, the structures damage identification based on vibration test is surveyed. Finally, the major research work of this dissertation is produced.In the second chapter, the structures damage identification methods based on FRF and GA is presented. GA is an important part of computation intelligence, compare with other mathematical methods, it has the characteristic of adaptive itself, robustness, and parallelism, so it can process the information with the uncertainty and noise, it is a typical global optimization method. if the input of structures is know, the testing of frequency response function(simplified in FRF) is simple and the precision is high, and it contains abundance information. The test FRF and the corresponding calculated FRF are used to construct the target function of GA, the damage of structures can be identified well in difference level noise in the examples.In the third chapter, based on the work of previers, a direct damage identification method of structures based on residual force vector is presented. Compare with the traditional method of residual force vector, the weakness that it can only identify the location of damage but not extent in generally directly is overcome. The stiffness matrix perturbation of the damaged structure is expanded by the stiffness connectivity matrix at first, then a new equation of residual force vector is got, it can be solve directly, so the analytical solutions of the stiffness parameter perturbation of elements are got. This method can identify the location and extent of structures damage at the same time only need one calculation step, and need only the first mode parameters of the damaged structures.In the fourth chapter, the damage identification of structures with insufficient output information is researched. In the direct damage identification method of structures based on residual force vector, when the output information is insufficient, the completed mode shapes can not be got, so the completed mode shapes can be got only by mode extend, the damage identification results based on extend mode shape depend on the complete degree of the test information of damage location. In the damage identification of structures base on GA, when the output information is insufficient, the insufficient test FRF is used to construct the target function of GA is presented, and GA is used to identify the structures damage. In the example of benchmark structure, the identify results is well.In the fifth chapter, the damage identification of structures with unknown input(excitation) information is researched. When the input is unknown, the errors of identification mode parameters are larger than known input in considering of test noise, and it lead to larger errors of damage identification results, in the example, the identification results is reliable only in considering a very low level noise. In the structures damage identification base on GA, when the input is unknown, the test FRF can not be got, if the spectrum of input is flat, and approximately to the white noise(such as fluctuating wind), it's the power spectrum is a constant, so the origin FRF of structures are similar to the power spectrum in form. So the target function of GA constructed by testing power spectrum and corresponding calculating FRF is presented, and used to identify the structures damage. In the example of benchmark structure, a good identification results is got. At last, the case considering with the unknown input and output incomplete is researched, only parts of test power spectrum and corresponding calculating FRF are used to construct the target function of GA, in the example of benchmark structure, the good identification results are got too.The last chapter summarizes conclusions in this dissertation, pointes out the present problems in the damage identification of structures, and narrates the prospect for the research work of future in this field.