| In order to fully develop the water energy resources which are rich in the western region of China,it is inevitable to build a number of high arch dams in the area of high seismic intensity,which inevitably brings many technical difficulties to the seismic construction of the dam.In previous studies,the input form of ground motion is assumed to be vertical incidence,which is not consistent with the randomness and multiplicity of actual seismic motion and will directly affect the reliability of calculation results.Therefore,in the seismic analysis of arch dam,such important factors as the input mechanism of ground motion with infinite ground damping,the nonlinear dynamic interaction between dam body,reservoir water,silt and foundation,and the oblique incidence of single and double seismic waves should be considered.In this paper,based on the finite element model of arch dam,the influence of the oblique incidence of the uni-directional input seismic wave on the arch dam system is deeply studied,and the seismic response of arch dam under the bi-directional seismic excitation is discussed and studied.The main research work is as follows:(1)In order to truly simulate the dynamic response of arch dam under the seismic action,the radiation damping effect of infinite foundation should be taken into consideration.And in the selected viscoelastic artificial boundary,analytical stress field corresponding to the incident wave field at the bottom boundary and the free wave field at the side boundary is regarded as the boundary load to realize the input of ground motion.Based on the boundary fluctuation input method above,the theoretical foundation of the reservoir-dam system,as well as consideration to the influence factors of silt at the bottom of reservoir,the dam body-reservoir water-silt-foundation coupling model is finally constructed.When oblique incidence of seismic wave is simulated,it is decomposed into the vibrational components in the transverse and vertical directions of the river,and the seismic response to the arch dam system model under different excitation angles is calculated.(2)In the study of oblique incidence of uni-directional seismic wave,three working conditions,namely,ground motion input of the downstream of arch dam,ground motion input of the upstream of arch dam and ground motion input of the base of arch dam,are respectively carried out.Firstly,in order to visually verify the necessity of the discussion on oblique incidence of seismic wave,representative reference points are selected from all parts of the dam body and the base of dam,and the displacement response and principal stress response of each reference point of the incidence Angle(0°,15°)in the x-direction and y-direction are analyzed.And then the incidence Angle can be expanded to 30°,45°,60° and 75°,so as to study the analysis on seismic stability of arch dam at different excitation angles,which proves that oblique incidence of seismic wave has a relatively significant influence on the displacement response and the main stress response of the arch dam system.The results show that there is a maximum,namely,the most adverse incidence Angle,which is adverse to the study on seismic stability as the incidence Angle is 45°.(3)In the aspect of bi-directional seismic wave,this paper adopts the method that studying vertical incidence of seismic wave and the vibration directions at different incidence Angles to analyze the seismic response of arch dam.The input form that seismic wave rotates around the coordinate system of arch dam to some angle is taken as a research means of this paper.So,it is concluded that the bi-directional seismic wave has the maximum of displacement or stress of dam body which is related to vibration excitation angles rather than traditionally appearing in the transverse and vertical directions of the river like the uni-directional seismic wave.The results show that the contributions of bi-directional seismic wave input to seismic evaluation of arch dam cannot be ignored since the seismic response influenced by bi-directional action is obviously greater than that influenced by uni-directional action. |
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