Research On Structural Damage Identification Based On Improved Sensitivity Method For Modal Parameters

The vibration-based method is an easy and quick method to damage identification. In the filed,highly effective studies have been done by domestic or overseas scientists, and many methods which detect damage through changes in modal parameters were advanced. A common analyzing method of structural identification is derived by sensitivity theory. Firstly, sensitivity matrix can be obtained according to the different sensitive degree which is based on the damage degree of different members or the same one of structural modal parameter. Then, it is viable that solve the damage state of the structure according to the one-to-one correspondence between the current states and establish the modal parameters variation before and after the structural damage according to the sensitivity. This is the principle of structural damage identification that using the sensitivity of modal parameters.In this paper, thorough research is carried out on the structure damage detection technique based on the sensitive degree of modal parameter. Detailed contents are summarized below:①The first and second order sensitivity matrixes of modal parameters that respect to the damage member are derived, and the modal truncation error which produced during the derivation of modal mode sensitivity is improved. Though the analysis of sensitivity matrix based on the beam structure, we could see that the sensitivity degree of high order modes to the damage is higher than the low order modes.②The first and second order sensitivity equations are established respectively based on the principle of taylor series expansion. And the solving method of these sensitivity equations was studied. In this paper, we solve the first order equation using generalized inverse technique, and also using trust-region reflective Newton method to solve the second order sensitivity equation.③Considering the fast solving speed by the first order sensitivity equation and the high solving precision by the second order equation, this paper puts forward a mixed iteration algorithm which is applied in structure damage detection. This algorithm uses the second order nonlinear analytical solution as the first substituting value, and then the first substituting value is modified based on the taylor series bias error using the solution of the first order sensitivity equation.④Programming the modal analysis program and damage identification program about the cantilever beam, continuous beam, plane cantilever truss, space truss, plane frame and space frame, which is based on the finite element theory about the beam structure, truss structure and frame structure. Damage identification is studied using the mixed iteration algorithm which is mentioned in this paper. It shows that the mixed iteration algorithm in this paper has a better convergence and a faster iteration speed because the higher precision second order nonlinear analytical solution is adopted.⑤Study on visualization which is based on the plane frame structure has been made, using the damage identification method. Then develop a plane frame structure identification system that could automaticly form the finite element model according to the model parameters and control parameters which user inputs. Furthermore, this system could make modal analysis and the damage identification could be carried out though the damage identification theory mentioned before by using modal analysis.