Modal Identification And Eigenvalue Finite Element Analysis Of Gravity Dam Based On Seismic Excitation And Response

Calculation of dynamic respoinse and eigenvalue of dam under earthquake vibration is the main work to study seismic performance of gravity dam.In the analysis of gravity dam vibration characteristics,seismic monitoring data of dam based on the input and output of two kinds of modal identification method for large hydraulic structures were identified and compared with the results of finite element calculation,has important research value.Modal identification is the characteristic frequency,damping ratio and mode shape of the structure,which is an important characteristic parameter of the structure,and reflects the inherent characteristics of the structure.In the finite element analysis,due to the interference of the boundary conditions of the model foundation,the analysis of the conventional finite element model is affected by the parameters such as the elastic modulus of the dam and the range of the foundation.Therefore,based on the modal parameters of gravity dams identified by seisimic record,adding lateral elastic dam base plane,establish the finite element model of water-dam-foundation with eigenvalue have great significance.The main work and conclusions are as follows:(1)Reading a large number of relevant documents at home and abroad,studied the modal identification method which is widely used in civil engineering and mechanical engineering.Then,combining with the actual engineering environment characteristics,analyzed several methods for pattern recognition of large structures under environmental excitation.In addition,describe the development of structural modal identification and the application of modal identification in hydraulic structures,and pointed out the problems existing in the analysis of large structural characteristics.At the same time,propose the dynamic response and modal identification method of concrete gravity dam for large hydraulic structures.(2)Discuss the pretreatment method of random decrement and NExT these two kinds of recognition,as well as discussed three types of modal identification methods in frequency domain,time domain and frequency domain and the advantages and disadvantages of each method.,derive the definition and correlation of frequency response function and impulse response function under different excitation;the properties of viscous damping and proportional damping in various degrees of freedom systems;the definitions of autocorrelation function,cross correlation function and white noise.(3)Focing on the two methods of data preprocessing,random decrement and NExT,introduce an improved method of random decrement based on acceleration signal,mainly studied the ARMA method based on the excitation and response signals and the ITD method based on the acceleration response signal,analyze the advantages and disadvantages of the two modal parameter identification methods in the identification process respectively.(4)Proposing a new idea of two joint algorithms for modal parameter identification,that is the random decrement-ARMA method and NExT-ITD method,the principle and process of its identification are described in detail,Through the calculation of the two degree of freedom example,the correctness and reliability of the two methods on the model frequency and vibration mode identification results are obtained,the identification of damping ratio is relatively accurate.(5)According to the measured seismic monitoring data of Shuikou gravity dam,selected the dam of 19th section as the object of study,identification of dam modal parameters by frequency spectrum analysis,random decrement-ARMA method and NExT-ITD method.Established a three-dimensional finite element model of gravity dams with corresponding eigenvalues,research the vibration characteristics under actual seismic records and the modal parameters identified by the model,compared and analyzed the results of the identification with the model identificate result which above mentioned,illustrated that the two identification methods in practical engineering is feasibility,it is also shown that the model can reflect the dynamic characteristics of gravity dams under earthquake.