The Studies Of Earthquake Input Models With The Consideration Of The Effects Of Dam-Foundation Interaction

With the drastic development of new structures, which are in high need of seismic safety analyses, the anti-seismic technology has experienced a sustained improvement. As an important infrastructure for the distribution of water resources nationwide, the more strict seismic design techniques for dams are needed. Therefore, more thorough and intensive study should be carried on to the seismic response of dams. Different input modes of earthquake ground motion have significant influences on the seismic design. Thus, the soil-structure interaction is needed to construct the infinite foundation model reasonably, and understand the feature and implementation of earthquake excitation. In the present study, by making use of two different earthquake ground motion input modes, i.e., equivalent inertial force model and earthquake input at foundation boundary, and the corresponding models for infinite foundation, the accuracy, the application to engineering practice of these models are studied.The features and extents of application for these earthquake input models are illustrated according to the comparisons and analyses of the seismic analysis of dam-foundation system.The main contents are as following:(1) The two models for infinite foundation, i.e., local viscous-elastic artificial boundary condition(VEABC) and dynamic stiffness computed by Scaled Finite Element Method, are used for the model of earthquake input at foundation boundary. According to the formulation of VEABC and the corresponding earthquake input scheme, the codes based on the ANSYS software are developed. The codes for the solution of the equilibrium equations in frequency domain for dam-foundation system are completed based on the dynamic stiffness of infinite foundation with SBFEM. The numerical examples for free field response in the elastic homogeneous half space and the scattered response of semi-circle canyon are computed to validated the accuracy of infinite foundation model, earthquake input scheme, and the codes.(2) The seismic analysis of the 2D gravity dam-foundation system and 3D arch dam-foundation system are performed for two kinds of the earthquake input schemes, i.e., the models of equivalent inertial force and earthquake input at foundation boundary. According to comparisons and analyses of the vibration properties of the dam body, relative displacements to the base of dam at different key points, stress distribution of dam body, to what extents the effects of different infinite models, earthquake input models will have on the seismic response,and the scope of the application and the features of these earthquake input models are summarized.a. The model of equivalent inertial force is simple with high efficiency, however, the simplification to the infinite foundation is too na?ve for considering the soil-structure interaction.b. In the earthquake input at foundation boundary model, the radiation damping of infinite foundation, the travelling phenomenon of earthquake wave and the changes of vibration properties of the dam can be taken into consideration. The scaled boundary finite element method can be used for compute dynamic stiffness of the infinite foundation and reflects the radiation damping with relatively high accuracy. So the accurate earthquake input load can be obtained under the assumptions of the earthquake input at foundation boundary model. The VSABC can approximately represents the radiation damping of infinite foundation in the low frequency ranges, and owing to the simple forms and decoupled property, the VSABC can be used for seismic analyses of large scale structure-foundation system.c. The change of free field response by the construction of dams which is realistic can not be taken into consideration for earthquake input at foundation boundary model. The earthquake input with interaction of upper structure should be developed in the future.