Research On Damage Identification Method Of Wharf Frame Structure Based On Dynamic Response

In the wharf construction of Chinese river port,the frame structure is widely used.Due to the long-term effect of various natural and man-made loads and natural environment changes,local damage and deterioration of the structure often occur.If it is not found and handled in time,it may lead to the overall damage of the structure.Therefore,the effective detection and identification of local damage of wharf frame structure is particularly prominent and critical.However,due to the complexity and uncertainty of the injury itself,the identification results of different parts,degrees and ways of injury are often different,which aggravates the difficulty of injury research and the ambiguity and non-systematic identification effect.In this paper,how to effectively identify the damage of wharf frame structure under the combined action of a variety of environmental loads is studied.The main research work is as follows:(1)Based on the mechanical characteristics and failure modes of the wharf frame structure,the structure generalization analysis model is drawn up.Then the finite element model of the wharf frame structure was established using ANSYS finite element software.The model was set as the non-destructive structure and the structure with the damage degree of 10%,20%,40% and 60% at 7 different damage locations.The position and loading mode of the loading load on the wharf frame structure were determined.The modal analysis of the wharf frame structure before and after damage is carried out,and the modal parameters are extracted and compared.The results show that the modal parameters are not sensitive to the damage of wharf frame structure.(2)The transient dynamic response of the finite element model is analyzed.Based on the change of acceleration response parameter,which is more sensitive to structural damage at the selected response observation points,the transient dynamic response rules of the structure before and after damage are summarized.The results show that the larger the damage degree is,the greater the change of the transient dynamic response parameters are.In addition,the acceleration responses of the front pile foundation of the superstructure and the middle and lower layers of the rear frame change more significantly due to structural damage.(3)Based on the wavelet packet energy analysis of the transient acceleration parameters,the damage identification index and damage location index were proposed.The results show that the greater the damage degree is,the more obvious the damage degree identification index based on the change rate of wavelet packet energy changes.The damage location index defined by the rate of change of the total energy difference of the acceleration wavelet packet between the intact structure and the damaged structure can locate locally the damage reduction location of the stiffness of the wharf frame structure clearly.(4)Taking the stiffness reduction rate as the structural damage degree parameter which can reflect the characteristics of the structure itself,the target function based on the residual difference of the damage degree parameter of the wharf frame structure is analyzed,and the inversion recognition model of the damage degree parameter of the wharf frame structure is proposed.The inversion analysis results show that the stiffness reduction rate of the parameter inversion is higher compared with the setting,and the higher the damage degree,the higher the inversion recognition accuracy and the more accurate the result.(5)The damage location indexes of different damage locations and different degrees of damage are treated as training samples after xgboost discretization,and a group of damage location indexes of different single and multiple damage locations under 50%damage degree are used as test samples.The damage location method is established based on the random forest classification algorithm(RFC),and the damage location analysis of the wharf frame structure is carried out.The results show that the damage location method of wharf frame structure based on xgboost-RF can locate single damage location and multiple damage location more accurately.(6)The structural damage degree identification index and damage location index are analyzed through the dynamic response model test corresponding to the damage condition,and the applicability and accuracy of the damage degree parameter inversion model and the xgboost-RF damage location method in the model test are verified.The results show that the damage degree identification index and damage location index defined in this paper can accurately identify the structural damage degree and damage location on the wharf frame structure test model.(7)Based on the transient dynamic response,the damage identification method of the wharf frame structure is constructed.The engineering realization process of the damage identification method of the wharf frame structure is proposed by summarizing the process steps of the structural transient dynamic signal acquisition,the transient dynamic response signal analysis and processing,the structural damage location analysis method and the structural damage degree inversion method.On this basis,the damage recognition system software of the wharf frame structure has been integrated.