Modal Parameter Identification And Seismic Response Analysis Of Gravity Dams Based On Seismic Records

Calculating the dynamic response of a dam under earthquake is an important work to study the seismic performance of a dam.Based on the seismic monitoring data of the dam,the modal parameters of large hydraulic structures are identified by modal identification technology,and compared with the results of finite element analysis.It is particularly important to establish a finite element model with corresponding characteristics to analyze the dynamic response of the dam according to the results of modal identification.Through with Shuikou gravity dam,this paper identifies the modal parameters of the dam by using the two time domain modal identification techniques proposed in this paper,which reflects the inherent characteristics of the structure.At the same time,a three-dimensional finite element model of reservoir-dam-foundation is established by using viscoelastic artificial boundary and dynamic finite element analysis method.The corresponding eigenvalues of the finite element model are calculated and studied,and checked with the results of modal identification method to verify the correctness and feasibility of the model.Then,the dynamic response of gravity dam under earthquake is preliminarily studied,which provides a correct and feasible theory for the seismic design of dam body,as well as the results of modal identification method.The dam has provided reliable technical support for its construction.The main contents of the thesis are as follows:(1)A large number of references at home and abroad were consulted to study the modal identification method widely used in civil and mechanical engineering fields and the relevant literature on Seismic Dynamic Analysis of gravity dams.At the same time,the development process of structural modal identification and the application of modal identification in hydraulic structures are expounded.(2)The preprocessing methods of random decrement and natural excitation for modal identification are introduced in detail.Prony method based on excitation and response signal and STD method based on acceleration response signal are discussed systematically.Two new methods of joint modal parameter identification are proposed,namely natural excitation-Prony method and random decrement-STD method.The principle and process of identification are described in detail.By calculating two-degree-of-freedom examples,the correctness and reliability of the identification results of model frequency and mode shape are obtained,and the identification of damping ratio is relatively accurate.(3)The application of three-dimensional finite element dynamic analysis method of viscoelastic boundary to gravity dam is introduced in detail.A three-dimensional linear finite element program DYCDAM.F for calculating dynamic response of gravity dam under earthquake action is compiled by FORTRAN language.(4)According to the measured seismic monitoring data of Shuikou concrete gravity dam,the typical 19 th dam section is selected as the research object,and the modal parameters of the dam are identified by modal identification method.A three-dimensional finite element model of gravity dam with corresponding eigenvalues is established to study its vibration characteristics and the modal parameters calculated by the model under the measured seismic records.The results are compared with those obtained by the above modal identification methods and verified each other.The feasibility of the two methods in practical engineering application is illustrated.It is also proved that the finite element model can reflect the dynamic characteristics of the dam under earthquake ground motion.(5)When the finite element model is used to calculate the dynamic response of the dam,considering that the circular frequency of modal identification coincides with that of the mass-free foundation model,the circular frequency of modal identification or the circular frequency of the mass-free foundation model are proposed to determine the Rayleigh damping in the equivalent nodal load input model of the mass foundation.The results show that the acceleration response of the dam calculated by the proposed method is between the equivalent nodal load input model of the mass foundation and the free field input model of the mass-free foundation,and is close to the free field input model of the mass-free foundation.