Study On Damage Identification Method Of Beam Structure Based On Curvature Mode

Bridge health monitoring is a hotspot and focus of research in the field of contemporary engineering.Its main function is to evaluate the operational status of bridges,avoid bridge accidents in time,and provide a basis for bridge maintenance and management decisions.Damage identification is a very important part of bridge health monitoring and the basis of health monitoring system.Therefore,it is necessary to study and analyze the damage identification method.As the derivation of the mode shapes,the curvature mode can amplify the local discontinuity of the mode shape caused by the structural damage,thus realizing the damage identification of the structure,which is a sensitive global damage index.In this paper,the simple supported beam and continuous beam are taken as the research object.Through theoretical analysis and numerical simulation,the bridge damage identification method based on curvature mode is studied.The main work and research results of this paper are as follows:(1)The theoretical basis of bridge damage identification method based on curvature mode is elaborated.The finite element model of simply supported beam and continuous beam are established by ANSYS,and the displacement modal shape is calculated.The curvature mode and its derived curvature modal difference index,curvature modal ratio index,average curvature modal damage factor(CDF)and instant curvature modal damage factor(DF)are used to identify the damage location of bridge structures under different working conditions.The effects of different noise levels on the curvature modal index are also considered.The analysis and comparison results show that the recognition effect,anti-noise and practicability of the curvature modal difference index are better than the other four indicators.(2)The theory of wavelet analysis is introduced and the damage identification of beam bridge structure based on the principle of wavelet singularity detection is studied.The curvature modal difference is used as the input signal,and the wavelet coefficients are obtained by wavelet transform of the input signal.The damage location is based on the transformed wavelet coefficients.At the same time,the singular Lipschitz index is used to judge the degree of structural damage,and the influence of damage degree,damage location,structural material and structural form on the Lipschitz index are explored.The analysis and comparison results show that the recognition effect based on curvature modal difference and wavelet analysis method is better than the curvature modal difference index,and further the experimental data is used to verify the applicability of curvature modal difference and wavelet analysis method in practical engineering.(3)Aiming at the situation that the initial mode is difficult to obtain in practical engineering,the concept of structurally intact curvature modal curve is proposed.The curve is constructed by least squares fitting method,and the damage degree of structure is studied by the effective area of damage.Furthermore,a recognition method based on bridge substructure is used,and combined with the intact curvature modal curve,the bridge is decomposed into simple sub-components according to the characteristics of each component that constitutes the whole bridge to realize damage location and damage degree identification.To some extent,it simplifies the recognition difficulty of large and complex bridges,and discusses the influence of the difference of unit division and section form on the recognition effect of curvature modal method.(4)Two new index of damage identification based on curvature modal analysis(frequency weight superposition curvature modal difference and frequency weight superposition curvature modal ratio)are proposed.Two new indexes are used to simulate the simple supported beam and continuous beam.By comparing the new index with the existing curvature modal index,it is found that the new index overcomes the problem that the modal nodes of each order of the traditional curvature modal index can not be identified,and the recognition effect is more obvious.The new index is used to quantitatively identify the damage degree,which solves the defect that the traditional curvature modal method can not accurately identify the damage degree of the structure.The effect of noise on the recognition results of the two new indicators is further considered,which verifies that the two new indicators have certain anti-noise ability and engineering applicability.