Research On Damage Identification Of Beam Structure Based On Perturbation Theory

During the service lives of the structure,the reduction of the structural strength and the accumulation of damages are unavoidable since affected by the various loads and sudden disasters.These diseases will lead to the decline of the normal working capacity of the structure,even cause damage or catastrophic accident to the structure.Therefore,structural damage identification is of great significance for ensuring the safe operation of the structure.Natural frequency is a global index to the whole structure,which has the advantages of simple testing and higher accuracy,so the structural damage identification method based on natural frequency has broad application prospects in practical engineering.In this dissertation,the beam structure is taken as the research object,combining perturbation theory with pattern recognition technology for structural damage identification,and a pattern recognition method is proposed to identify the single and multiple damages of the beam structure.The main research contents are shown below:(1)Using the perturbation theory,the effect of changes in local parameters(stiffness,mass)of the structure on natural frequencies is studied.The study shows that when the local mass and local stiffness of the structure is changed,the square change of the natural frequency of the structure is directly proportional to the square of the modal shape and the curvature mode where the parameter changes.When the structure is damaged,the local mass change is smaller than the overall mass,so it is considered that the mass is constant and only the stiffness changed.Therefore,the relationship between the square change of the natural frequency of the structure,the stiffness change,and the curvature mode is used as the theoretical basis for damage identification.(2)According to the theoretical basis of structural damage recognition,pattern recognition technology is applied to establish a structural damage pattern recognition method.First,Accurately the build structural finite element model,and the damage mode vector is constructed using the numerical calculation results.Then the actual damage feature vector is established based on the natural frequency of the damaged structure.Finally,the similarity between the mode vector and the feature vector is measured by the Euclidean distance function.When the normalized Euclidean distance is 1,the location and degree of damage to the structure can be accurately identified.The damage identification method is studied with simply-supported beams and cantilever beams respectively,and a mass-addition method is proposed to solve the problem that the damage results of simply-supported beams are not unique.(3)The reliability of the damage identification method was researched through a damage identification test.Experimental study on single damage identification of simply supported beams.The mass addition method was used to change the symmetry of the structure,and accurately identify the damage location and damage degree of simply supported beams;Experimental research on single and multiple damage identification of a cantilever beam,and accurately identify the location and degree of cantilever damage.When multiple damages occur,the natural frequency change is the cumulative result of changes everywhere.The damage recognition method is similar to the single.