Seismic Vulnerability Analysis Of Concrete Dams Based On Displacement

Seismic load is one of the main disasters that cause damage to concrete dams,so it is of great significance to carry out research on seismic safety of concrete dams.Seismic vulnerability analysis can predict the probability of concrete dams damaged to different degrees under different horizontal seismic loads.It can provide a basis for seismic safety evaluation,damage loss estimation and seismic fortification of dam structures.In view of the problems existing in the vulnerability analysis of concrete dams,such as high sensitivity of resistance index parameters,difficult to obtain and difficult to quantify the classification of earthquake damage grade,the displacement of concrete dams is selected as resistance index,and the corresponding classification criteria of earthquake damage grade are determined.A displacement-based seismic vulnerability analysis method for concrete dams is established.The main research contents are as follows:(1)Irn view of the long pretreatment time of viscoelastic artificial boundary in the nonlinear dynamic time history analysis of concrete dams,the simulation of viscoelastic artificial boundary based on thin layer element is proposed.The thin-layer element theory is combined with viscoelastic artificial boundary theory,and the equivalent viscoelastic boundary element is constructed by the thin-layer element according to the principle of matrix equivalence.By setting parameters of equivalent viscoelastic boundary element in finite element software,viscoelastic artificial boundary is simulated.Finally,an example of a concrete gravity dam is given to verify the accuracy of the method.The results can be used for reference in seismic analysis of hydraulic structures.(2)Latin hypercube sampling and numerical method are combined to construct seismic vulnerability curve of dam-foundation system.The input of ground motion is measured seismic waves with different magnitudes,and the uncertainty of dam and foundation material parameters is considered by sampling.The cumulative sliding position of the dam toe along the foundation surface is selected as the seismic performance index,and the criteria for dividing magnitude 3 earthquake damage are given,namely,slight damage,medium damage and serious damage,and the corresponding performance levels are respectively,and.The sensitivity of uncertainties(peak acceleration,friction coefficient of contact surface,elastic modulus of foundation and tensile strength of dam concrete)in vulnerability analysis was analyzed by orthogonal test.Through this method,the vulnerability probability of gravity dams under various magnitude earthquakes can be calculated,and the sensitivity analysis of relevant parameters can be carried out,which provides scientific basis for seismic design and seismic fortification of gravity dams.(3)Based on the approximation ability of the nonlinear function of the discrete robust learning machine,a vulnerability analysis method for arch dams is proposed,which greatly reduces the number of dynamic time history analysis and improves the efficiency of vulnerability analysis for concrete dams.In the vulnerability analysis of a concrete dam,on the basis of considering the uncertainties of seismic ground motion,random variables such as friction coefficient of transverse joints,elastic modulus of foundation and tensile strength of concrete of dam body are taken into account,which improves the situation that only seismic ground motion is considered im the vulnerability curve of arch dam in the past.At the same time,the vulnerability curve established by combining extreme learning machine with Monte Carlo simulation has higher accuracy and more engineering reference value.