Damage Localization And Time-varying Damage Detection Of Beam Structures Based On Wavelet Energy

Real bridge structures in service are prone to damage due to the influences from external loads,environmental effects,disasters,and human effects.Therefore,it is necessary and urgent to conduct structural health monitoring and safety assessment on existing bridge structures,leading to a guarantee of structural safety,integrity,applicability and durability.As such,with a consideration of characteristics of bridge structure and service environment,this study introduces the theory of wavelet energy and detects the changing dynamic characteristic parameters in the process of structural damage at first.Then,various damage indices are established on a basis of these variant characteristic parameters.Finally,the accuracy and effectiveness of proposed damage indices are verified via a numerical example and two experimental tests.The purpose of this study is to progress on the methods of time-varying damage identification and damage evolution trend tracking of bridge structures,which will provide the basis and foundation for better understanding the mechanism of major bridge catastrophe,health monitoring and safety assessment.Thus,this study has a significant impact in both theory and practical engineering.The main contents and conclusions of this study are drawn as follows:(1)The analytical mode decomposition theorem(AMD)is first used to extract various intrinsic mode functions(IMF)from structural acceleration response signals.Then,the wavelet coefficients are calculated by wavelet transform and wavelet packet transform to construct the wavelet total energy change(WTEC),the improved wavelet packet energy curvature difference(IWPCD)and the wavelet power spectral entropy(WPSE),respectively.These three indices can be utilized to localize damages and identify damage degree.(2)On the basis of the successful identification of the damage location,the signal at damage positions are used as target signals.Then,fast independent component analysis(FastICA)is introduced to propose the time-varying damage index of wavelet energy change rate(WECR).In addition,the instantaneous modal curvature is also presented by a combination of displacement responses and principal component analysis(PCA).Finally,the proposed two indices can be used to identify time-varying damage,that is,the structural damage evolution process.(3)The feasibility and accuracy of the proposed indices are verified by a numerical example of a simply supported beam bridge model.In contrast,a simply supported steel beam with sudden stiffness reduction and a simply supported aluminum beam with linear stiffness reduction,are designed to investigate the feasibility and accuracy of the proposed indices,respectively.The results demonstrate that the proposed time-varying damage indices are capable of tracking structural time-varying damage of a beam structure with the premise of successful damage localization by damage localization indices.