Structural Damage Identification Based On Improved Empirical Wavelet Transform And Hilbert Transform

The safety operation of structure is inseparable from the structure health monitoring system in the operation of building structure.Once a component of the building structure is damaged or its function fails,it will inevitably lead to economic losses and casualties.Regular monitoring of structure performance and component quality is an effective way to reduce engineering accidents.Structural parameter identification plays a vital role in civil engineering health monitoring.Time-frequency analysis methods are widely used in structural parameter identification.However,classical time-frequency analysis methods such as Wavelet Transform and Empirical Mode Decomposition（EMD）have some defects in modal parameter identification of civil structures.This article will review the research status of various damage identification methods.Through comparison,Empirical Wavelet Transform（EWT）is selected as the basic method of civil structure modal parameter identification,and the deficiencies of EWT in spectrum division are improved.Which makes the improved EWT more suitable for the recognition of modal parameters of civil structures.At the same time,The Hilbert Transform（HT）is performed on the EWT decomposition Signal,and two sets of damage indicators are constructed based on the Hilbert energy spectrum.The damage index realizes the damage identification of the civil structure,and the specific process is as follows:1.Local Maximum Synchrosqueezing Transform（LMSST）was used to improve the spectrum partitioning of empirical wavelet Transform.Aiming at the over-decomposition problem of adaptive spectrum partitioning of empirical wavelet,the time-spectrum of LMSST is proposed to calculate the filter boundary value,which is used to improve the spectrum partitioning of EWT,and an improved EWT algorithm is obtained.The improved EWT algorithm is used to separate and verify the simulated synthetic signals,and the results show that the fitting accuracy of the decomposed signal component and the real signal component is more than 95%.2.Two damage indices based on Hilbert spectrum were constructed.In order to realize the damage identification,need to improve the EWT decompose signals for further processing,based on the Hilbert transform of the decomposition of signal processing,get the signal component Hilbert instantaneous energy spectrum,and the marginal spectrum,the instantaneous energy spectrum marginal spectrum and the marginal spectrum characterize the change characteristics of energy in the direction of time and frequency respectively.After the structure is damaged,its energy value will decrease,but when the component is partially damaged,its energy change accounts for a small proportion of the energy of the entire component itself,that is,it is not easy to distinguish the damage.Therefore,the instantaneous energy spectrum and the marginal spectrum integrates the time and frequency directions respectively to obtain the energy curve E and the energy curve SES that are easier to distinguish damage.Only by comparing the energy curves before and after the damage,the damage can be clearly distinguished.At the same time,the damage index DI₁ is constructed according to the energy curve E,and the damage index DI₂ is constructed by the energy curve SES.The quantification of structural damage is achieved through these two damage indicators.3.Experimental verification.The IASC-ASCE-Benchmark four-layer framework model is used to test the feasibility and effectiveness of the proposed damage identification method.The experimental results show that the proposed method can identify different locations and different degrees of damage even under environmental excitation;At a noise level of 20%,this method also exhibits strong robustness.In summary,from the perspective of energy,this paper applies improved Empirical Wavelet Transform and Hilbert Transform to structural damage identification.This method has important theoretical significance and practical value.