Research On Framed Structures Damage Identification Based On Moving-window Least Squares Fitting Meth

The aging of the structure and the local damage are inevitable problems in the course of normal use.An accurate identification of the location of structural damage can effectively avoid as much heavy casualties and property losses caused by sudden destruction of the whole structure and collapse as possible,so the structure damage identification is very important in the field of civil engineering.In the methods of structural damage identification,the method of using vibration characteristics curvature to identify damages has the advantages of convenient data acquisition and good local damage identification.This method often uses second-order central difference method to obtain the curvature data,which leads to the defect of the edge node data loss and the poor noise immunity ability.This paper puts forward a damage identification method based on moving least squares fitting method and vibration characteristic curvature.This method uses the moving least squares fitting method to fit the nodal data equation of the vibration characteristics,and then obtains the curvature of the vibration characteristic.Therefore,the proposed method not only retains the advantage of the structural damage identification by using the vibration characteristics,but also overcomes the disadvantages of the traditional second-order central difference method.In this paper,the damage identification of a typical truss structure and a orthogonal pyramid space gride structure is presented,the results are as follow:1.moving-window least squares fitting method obtain the vibration characteristics of the curvature with better noise immunity performance than the commonly used method of the two order difference method,and does not lose the edge node data.2.The single damage curvature vibration characteristics obtained by moving-window least squares fitting method can effectively identify the location of each position of the truss structure,and if the modal curvature difference method and the flexibility curvature method uses the first modal displacement for calculation,it can obtain the best recognition results;but for detection of multiple damages,modal curvature difference method,the flexibility curvature method and the generalized displacement curvature cannot effectively identify the brace damage,but the frequency response function curvature difference method can not only identify the all brace damages,but also can be used for quantitative identification of damage.3.Noise analysis of truss structure shows that the modal curvature difference method and flexibility curvature method both have poor noise immunity performance,but the frequency response function curvature difference method and the generalized displacement curvature method can effectively eliminate the influence of noise in the process of obtaining the damage data,so it has good noise immunity.4.For damage identification of orthogonal pyramid space gride structure,the vibration characteristics of simple differential curvature has many false alarms.This paper introduces wavelet analysis to process the damage identification data,using the reconstructed wavelet coefficients to identify the damage.The simulation results show that the method can accurately identify the single damage and multiple damages of the grid structure.5.For damage identification of orthogonal pyramid space gride structure,the vibration characteristics of simple differential curvature has many false alarms.This paper introduces wavelet analysis to process the damage identification data,using the reconstructed wavelet coefficients to identify the damage.The simulation results show that the method can accurately identify the single damage and multiple damages of the grid structure.6.The analysis of the noise immunity performance of the grid structure shows that,among those vibration characteristic index in this paper,the frequency response function curvature difference method has the best noise immunity performance,and has a good effect on identifying the slight damages.