Study On Damage Detection Method Of Structures Using Incomplete Modal Information

Damage identification is a core content of the structural health monitoring system.It plays an important role in the safety early warning,life assessment,maintenance and reinforcement of large-scale engineering structures.In practical projects,due to the limitations of the number of sensors and measurement conditions,only limited measuring points can be monitored,and the measurement data is usually interfered by noise.In this paper,based on incomplete modal information with noise,the sensor layout scheme is discussed,and a two-stage damage detection method is proposed.The damage locations are roughly confirmed at first,then the damage location and damage degree are accurately calculated.The main results are listed as follows:(1)Based on the cross-model cross-mode(CMCM)method,an improved CMCM method is proposed to reduce the influence of various types of errors.For the limited measure point problem,the minimum modal error(MME)method is used to expand the incomplete mode shape,and the two methods are combined to propose an improved CMCM-MME method.An example of a planar truss structure shows that under the conditions of finite measure points and noise interference,the structural damage location can be confirmed only by solving linear equations.(2)Common sensor placement methods and evaluation criterias are introduced.Different sensor placement schemes for truss structure are used in damage detection to compare their damage identification ability.The results show that the EIF method works well with the damage detection method proposed in this paper.(3)A model updating method based on the improved CMCM method is proposed to identify the degree of damage.Incomplete mode shapes are expanded with parameterized expansion matrix based on dynamic condensation method,and constraint equations are established based on the improved CMCM method.The Hestenes-Powell extended Lagrange multiplier method is adopted to solve this constrained optimization problem.According to the optimal solution of the optimization problem,the locations and degrees of damage are judged.(4)For three-dimensional space structures,structural damages have different effects on different characteristics of the cell section(pull,pressure,bending resistance,torsion resistance).Based on the parameters of the finite element model,the damage is represented by the reduction of the physical parameters of the model,and different damage coefficients are separ ately set and solved.The proposed damage location method and damage quantification method are extended to three-dimensional space structure.The effectiveness of the proposed method is verified by a three-dimensional spatial structure example.