Seismic Fragility Analysis Of High Concrete Arch Dam

Many concrete arch dams built and under construction in the strong earthquake area of Southwest China are over 200 meters high or even 300 meters high.Once these high dam reservoirs are damaged in strong earthquakes,their functions of flood control,power generation and shipping will be affected.Once these high dam reservoirs break,serious secondary disasters will occur in downstream areas.Therefore,it is necessary to study the seismic performance of high arch dams under strong earthquakes and evaluate the seismic safety of high arch dams with reasonable methods.Seismic fragility analysis of arch dams can predict the probability of failure of arch dams under different intensity earthquakes,and then provide a scientific basis for performance-based seismic safety evaluation and decision-making.Therefore,it is of great significance to study the seismic fragility of arch dams.In this paper,performance indices,intensity measures and efficient calculation method for seismic vulnerability analysis of high concrete arch dams are studied.Some achievements with scientific significance and engineering application value are obtained.The main research contents are as follows:（1）On the basis of the displacement of crown cantilever,another two performance indices（contraction joints opening and damage volume ratio）are suggested.Considering the uncertainties of earthquake and material,the incremental dynamic analysis of arch dam is carried out by taking the spectral acceleration₍（6）（₁）of the stream component as seismic intensity measure and arch crown displacement,contraction joints opening and damage volume ratio as performance indices.The seismic damage grade of arch dam is classified and the limit states of performance indices are determined.The probabilistic seismic demand model is established by fitting the results of incremental dynamic analysis,and then the seismic fragility curves are obtained based on the three performance indices.These fragility curves reflect the fragility of arch dam from different levels and angles.（2）Two vector-valued intensity measures（VIMs）for seismic fragility analysis of arch dam are proposed.Based on VIMs,seismic fragility surfaces of arch dam are established with three performance indices,namely arch crown displacement,contraction joints opening and damage volume ratio.The range of independent variables of seismic fragility surface is studied,and the efficiency of VIMs and scalar intensity measures（SIMs）is compared and analyzed.The research results show that the probabilistic seismic demand model established based on VIMs can significantly reduce the dispersion of seismic demand.The seismic fragility surfaces based on VIMs can effectively reflect the change of failure probability caused by multiple intensity measures,and then the seismic performance of arch dam can be evaluated more accurately.（3）The response surface method is applied to seismic fragility analysis of arch dam,which improves the efficiency of fragility analysis.Based on the central composite test design method,the material-seismic intensity samples are established.The response surface model with arch crown displacement as performance index is obtained by finite element calculation of the samples,and then the accuracy of the response surface model is verified.To obtain the seismic fragility curves,the intensity measure₍（6）（₁）is chosen to be 0.1¹.2g,with an interval of 0.1g and a total of 12 intensity levels.For each seismic intensity level,the arch crown displacement corresponding to 100 sets of different material samples can be calculated by algebraic operation of the response surface model,which avoids 1200 times of nonlinear dynamic calculation of arch dam,thus the efficiency of fragility analysis is improved greatly.