Research On Damage Detection Methods For Structures Based On Strain Modes

As a key step in structural health monitoring,damage detection has been studied for decades.And,vibration-based damage detection methods play a vital role in structural health monitoring,but there are many problems in the application of those traditional damage detection methods,for instance,the ability to promptly sense and accurately locate realistic damage in structures are the primary challenges confronting traditional damage detection methods.Strain modes typically have high sensitivity in structural damage detection.Thus,damage detection methods for structures based on strain modes have been studied in this dissertation.Moreover,three damage indices were discussed to demonstrate the validity of the proposed method in experiment.The details are as follows:(1)According to the relationship between strain and displacement,strain modes was deduced.And,it was demonstrated that the strain mode has the advantage of high sensitivity to local damage.Moreover,the natural excitation technique based on the strain response combined with the eigensystem realization algorithm was applied to identify the strain modal parameters of structures under ambient excitation and the flowchart of the method was provided.(2)In this dissertation,the identification accuracy of the natural excitation technique/eigensystem realization algorithm method based on strain response data is verified by the experiments of a steel cantilever beam.Next,three new damage detection indices: enhanced strain mode shape,enhanced strain mode shape possibility and strain mode shape curvature change were put forward and single-damage and multi-damage cases with different degrees and locations were prefabricated experimentally.The results demonstrated that all damage cases were detected in a reasonable manner,thereby demonstrating the validity of the proposed method in structural damage detection.(3)In order to eliminate the noise effect,the singular value decomposition combined with stabilization diagram was utilized in the eigensystem realization algorithm,as are the probability theory and the average process that are used in the damage indices.Three damage cases were successfully detected adding noise.Hence,the proposed method has a good ability to resist noise.Moreover,the detection range of a strain gauge is limited in the gauge length or adjoining range in experiment.Hence,it is necessary to optimize the instalment of strain sensors in practical use.