Study On Seismic Damage Process Mechanism And Quantitative Evaluation Criteria Of Concrete Dam-foundation System Based On Parallel Computation

In view of the importance of seismic safety of high dams and large reservoirs, relying on the subject on earthquake damage and failure of high dam-foundation system-part3of the key consulting project of the Chinese Academy of Engineering-seismic safety of high dams and large reservoirs in the western earthquake district, in close connection with the actual engineering earthquake cases, for the key and basic problem of strategic emphasis on damage process of high concrete dams under the input of exceeding design ground motion, the main innovation is made as follows in this paper.(1) Based on the nonlinear dynamic analysis model of high concrete dam seismic response that is closer to the actual situation(including dam-foundation-reservoir dynamic interaction, contraction joint opening and closing, radiation damping due to energy dissipation to the far field foundation, various types of terrain and geological structure in the near field foundation, non-uniform motion input to the foundation), under the input of exceeding design ground motion, the analysis model and solving method of considering nonlinear damage process of dam and foundation is presented.(2) Taking damage mechanics theory based on the damage variable as theoretical basis, a new damage model and solving method is presented that sets up the damage evolution constitutive relation directly based on the whole curve of dam concrete damage stress-strain process of tensile and compressive test results. The new method considers the unloading residual deformation, the constitutive relation difference of tensile and compressive damage evolution and the interaction of complex stress state in the actual dam under earthquake cycling load, preventing the uncertainty and complication due to the coupling of plasticity mechanics and damage mechanics. The characteristic length of model mesh size is considered to prevent mesh sensitivity of simulation results.(3) In order to check the model, calculation method and simulation result, the actual seismic damage of Konya gravity dam and Shapai arch dam is investigated and interpreted. Koyna gravity dam in India experienced strong earthquake in1967, and Shapai RCC arch dam experienced exceeding design earthquake in2008. Compared with simulation results of various models applied in dam body concrete and foundation rock mass, the model presented by this paper is much closer to the actual seismic damage. In the case study of Koyna seismic damage, the ground motion input is determined by the strong motion record of foundation. In the case study of Shapai arch dam seismic damage, the ground motion input which is non-stationary both in amplitude and frequency is determined by stochastic finite faults method based on area source model in Wenchuan and the parameter correction by the existing strong motion record. The dam concrete strength is determined by measuring dynamic strength of the specimen obtained from the dam body by drilling hole. In order to accord with practical situation, the situation of air temperature, water temperature, water level, contraction joints and induced joints is determined by the situation at the time of earthquake.(4) Since the contact and material nonlinear model is very complex in the whole dam-foundation-reservoir system, enormous computational work is needed. The Shapai arch dam contains404090elements,425568nodes,2112contact point pairs, and more than1200000degrees of freedom; what’s more, the duration of ground motion input is long caused by earthquake rupture process in Wenchuan, so the conventional serial computation can not meet the engineering requirement. To this end, the introduction of parallel computing technology is necessary. The entire system is decomposed into several parts by domain decomposition method, making full use of the existing multicore computer, and the computation time is much shorter, with the operability of promotion and application in practical engineering design. The serial and parallel computing software applied in this article is independent development achievement, providing a powerful means to reveal seismic damage process of high dam system.(5) Current seismic calculation model ignores the mountain above dam crest. To compare the effect of two banks of mountain above dam crest, considering dam and foundation as elastic material, preliminary simulation on the impact of two banks of mountain acceleration response due to ignoring the mountain above dam crest is made.