| In the western China,numerous high concrete rockfill dams(CFRDs)with 200-300m have been built or plan to be built because of its abundant hydropower resources.However,this area is located in the Himalayan-Mediterranean earthquake zone,where the geological conditions are relatively complex,the earthquake intensity is high and the seismic activity is relatively frequent.Therefore,the research on dam safety subjected to earthquake excitation is of great significance.In addition,there are no high dams over 200m suffering from strong earthquakes,which can provide reference for seismic design and research.Consequently,it is of great scientific significance and engineering value to study the seismic safety of high CFRDs under earthquakes deeply,especially under strong earthquakes.Performance-based seismic safety evaluation method can analyze the structural performance changes under earthquake action comprehensively and deeply,and can estimate the risk of structures effectively,and it has been gradually applied in many engineering fields.However,the traditional deterministic analysis method is mainly used to evaluate the seismic safety of earth-rockfill dams at present,and the study of performance-based seismic safety evaluation is still in its infancy,especially for the high CFRDs.There are three main aspects which should be paid attention to.The real response behavior of structure under earthquake should be presented based on effective seismic analysis model and method.All kinds of uncertainties should be considered,and the seismic response should be analyzed from the probability perspective in practical work.Moreover,reasonable performance index and quantitative performance target are the prerequisite and foundation for seismic safety evaluation.To solve the above problem,this paper tries to establish the framework of performance-based seismic safety evaluation of high CFRDs from the perspective of stochastic dynamics and probability,combining the advanced seismic numerical simulation method and probability analysis method.In addition,the randomness of ground motion,damming material and their coupling randomness are synthetically considered.For this purpose,the generating method of stochastic ground motion based on the code for seismic design of hydraulic structures is proposed.In addition,the generating methods of random samples with high dimension and ground motion-material parameter coupling samples are also established.The seismic response characteristics of high CFRDs are revealed from the perspectives of stochastic dynamics and probability combined with the refined nonlinear finite element dynamic time history analysis method,generalized probability density evolution method(GPDEM)and fragility analysis method.The performance index and corresponding performance level with probabilitistic guarantee are also suggested for seismic safety evaluation of high CFRDs considering dam deformation,faced-slab safety and slope stability.Finally,the multiseismic intensity-multiperformance target-failure probability relationship is established,and the framework of performance-based seismic safety evaluation is preliminarily developed,which can provide scientific basis for seismic design and ultimate seismic capacity analysis of high CFRDs.The main work of this paper is as follows:(1)The necessity of establishing performance-based seismic safety evaluation method based on effective probability analysis method is pointed out on the basis of summarizing the existing uncertainty in earth-rockfill dams.The shortcomings of existing stochastic dynamic response and traditional probability analysis methods for earth-rockfill dams and their future development directions are reviewed.In addition,the theoretical basis and solution flow of GPDEM are described in detail.A stochastic ground motion model based on spectral expression-random function and a high dimensional random variable generation method based on GF-deviation optimization point selection technique are established.The validity and reliability of the GPDEM for nonlinear complex geotechnical engineering are verified by stochastic dynamic and probabilitistic analysis,which lays the foundation for subsequent stochastic seismic response analysis and performance-based seismic safety evaluation of high CFRDs.(Chapter 2)(2)The dynamic response and probability characteristics are revealed subjected to stochastic earthquake excitation,and the performance-based seismic safety evaluation method is established,combined with the elastic-plastic analysis of the CFRD dams.Firstly,a non-stationary intensity-frequency stochastic ground motion model,based on orthogonal expansion theory and spectral expression-random function method,is introduced to generate a set of acceleration time history with complete probability characteristics.Then,the response characteristics and distribution of dam acceleration,deformation and faced-slab stress are revealed from the perspective of stochastic dynamics and probability based on the GPDEM and the generalized plastic model,which can provide references for seismic response and ultimate seismic capacity analysis of high CFRDs.Finally,reasonable performance indexes are proposed and corresponding performance levels are divided based on the dam deformation and the faced-slab safety.In addition,performance-based seismic safety evaluation method of high CFRDs is established combining with fragility analysis.(Chapter 3)(3)The influence of material parameter randomness on dynamic response and seismic safety of high CFRDs is studied from the perspective of stochastic dynamics and probability.Firstly,the main random variables of elastic-plastic model parameters are selected for stochastic dynamic and probabilistic analysis by parameter sensitivity analysis.Then,the elastic-plastic random parameter samples are generated based on GF-deviation optimization point selection method.Finally,the similarities and differences between the responses caused by the randomness of material parameters and the randomness of ground motion are revealed,and the influences of different distribution types of random parameters are compared.In addition,the influence of different distribution types of random parameters is compared,and the influence characteristics of material parameter randomness and distribution types are studied subjected to deterministic seismic excitation.(Chapter 4)(4)The stochastic dynamic response and probability distribution of high CFRDs considering the coupling randomness of ground motions-material parameters are studied systematically,and the framework of performance-based seismic safety evaluation is perfected.Firstly,stochastic acceleration time history and random material parameter samples are generated simultaneously by combining spectral expression-random function and random variables of material parameters.Then,the stochastic dynamic response and probability characteristics of high CFRDs under the coupling random action of ground motion-material parameters are studied in detail,and the relationship between different randomness is revealed by comparing the stochastic dynamic and probabilitistic results which are caused by stochastic seismic ground motion and random material parameters.Finally,the performance relationship of multiseismic intensity-multiperformance target-exceedance probability and fragility curves are established considering the coupling randomness of ground motions-material parameters under different earthquake intensities,and the framework of performance-based seismic safety evaluation is improved.(Chapter 5)(5)The stochastic dynamic response of three-dimensional(3-D)high CFRDs is studied,and the faced-slab failure performance index and performance level based on the overstress volume ratio combined with the overstress cumulative time are emphatically discussed,which further improves the framework of performance-based seismic safety evaluation.Firstly,the variation and distribution of the dam acceleration,the deformation and the faced-slab stress are revealed from the perspective of randomness based on the aforementioned research results considering the randomness of ground motion combined with 3-D elastic-plastic analysis and probability analysis.The response distribution and range has certain reference significance for seismic safety evaluation and ultimate seismic capacity analysis of high CFRDs.Then,the performance index based on faced-slab overstress volume ratio combined with cumulative time is preliminarily investigated,and the corresponding performance level of seismic safety evaluation is suggested.Finally,the framework of seismic safety evaluation based on the dam deformation and the faced-slab safety is established by three-dimensional elastic-plastic stochastic dynamic results.(Chapter 6)(6)For dam slope stability,the framework of performance-based seismic safety evaluation of high CFRDs is systematically investigated from the perspective of stochastic dynamics and probability subjected to multiple random factors based on the finite element dynamic time history method considering the softening effect of rockfill.Firstly,it is revealed that the softening effect of rockfill will have a great impact on the dam slope stability by stochastic dynamic and probabilitistic analysis subjected to earthquake especially strong earthquake excitation,and it is unreasonable to investigate the dam slope stability only using the minimum safety factor.Then,the dynamic response of dam slope stability is investigated and compared based on the safety factor(Fs),the cumulative time of Fs<1.0 and the cumulative slippage,considering the randomness of ground motion,the uncertainty of material parameters and the coupling randomness of ground motion-material parameters.The stochastic dynamic and probabilistic results show that the three kinds of randomness all have certain degree of influence on the dam slope stability.Therefore,it is necessary to give full consideration to all kinds of uncertainties in order to establish the corresponding performance evaluation standard.Finally,the performance levels of dam slope stability safety evaluation is proposed based on of Fs<1.0 and cumulative slippage,and the performance relationship of multiseismic intensity-multiperformance target-exceedance probability and fragility curves are established considering different random factors,so as to the framework of performance-based seismic safety evaluation for high CFRDs is further improved.(Chapter 7)... |
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