Modal Parameter Identification And Their Uncertainty Quantification Of Ambient Excited Structures

The safety of engineering structures has been widely concerned worldwide.As a n important research field of civil engineering,structural health monitoring technology has also been developed rapidly in recent years.Structural modal parameter identification is an important topic in the field of structural health monitoring.It is very necessary and important to analyze the dynamic characteristics of engineering structures,especially large engineering structures(such as long-span bridges,super high-rise buildings,etc.),and the modal parameters of the structure are the basis of structural dynamic analysis.Structural modal parameter identification is also widely used,including model updating,structural response prediction,structural vibration control and structural dynamic system optimization.Structural modal parameter identification methods can be divided into traditional modal identification method using artificial excitation and modal parameter identification method under ambient excitation according to the excitation source.The modal parameter identification method under ambient excitation has been applied more and more due to its simple operation and low cost.In addition,it should be noted that due to the influence of factors such as measurement noise,excitation variation,mathematical modal error and numerical calculation accuracy in the process of structural modal parameter identification,the identification results of modal parameters often involve uncertainties.Therefore,the uncertainty quantification of the modal parameters in the statistical sense is particularly important.After the review of structural modal parameter identification theory,a new method for modal parameter identification is proposed in this thesis,which consider the uncertainty of modal parameters as well.According to the proposed approach,modal parameters of a numerical simulation structure,an experimental model structure and an actual engineering structure are studied respectively.The main research contents and achievements are summarized as follows:(1)The importance of the study of structural modal parameter identification for engineering structure is elaborated,and the advantages of ambient excitation relative to traditional artificial excitation are analyzed.The general situation of the modal parameter identification method is summarized.The reasons and significance of the study on parameter uncertainties are discussed in detail.(2)The main methods of modal parameter identification are systematically reviewed and theoretically analyzed.Extreme-point symmetric mode decomposition(ESMD),which is the theoretical basis of the proposed approach for structural modal parameter identification in this thesis,is introduced.Time domain analysis methods(NExT-ERA,SSI)and Frequency domain decomposition methods(PP,FDD)are also introduced in detail.(3)The algorithm of the ESMD-based modal parameter identification method proposed in this thesis is introduced.The proposed method is applied to analyze the modal parameters of a 5-storey numerical shear frame under a wind load and a 3-storey experimental steel frame under a random base excitation.The results show that the modal parameter identification results of the proposed method agree well with the theoretical solutions and the modal parameter identification results obtained by EMD method and NExT-ERA method,which verifies the feasibility and accuracy of the new method.The new algorithm also has good noise immunity.(4)In view of the uncertainty in the process of modal parameter identification,a method for the uncertainty quantification of the identified modal parameters is proposed,which is applied to analyze numerical model and experimental model respectively.Not only the best estimate of the modal parameters(mean)is obtained,but also its uncertainty(variance)is quantified..The statistical results show that with the increase of the modal order,the degree of dispersion of the modal parameter identification result increases gradually,and the uncertainty of the identification result of the damping ratio is larger than the uncertainty of the identification result of the frequency.(5)The vibration response of the main girder and the stay cable of Hongshan Bridge in Changsha were measured by wireless sensing technology.The proposed structural modal parameter identification method combined with uncertainty quantification method is employed to analyze modal parameters of Hongshan Bridge.The mean and variance of the first five modal parameters(frequency,damping ratio and modal shape)of the main beam and the frequency and damping ratio of the S09 cable are obtained respectively.The feasibility and accuracy of the proposed method are further verified by comparison with related research results.