ارزیابی ایمنی لرزه‌ای برای سدهای وزنی بتنی Seismic Safety Evaluation For Concrete Gravity Dams

For the aseismic reinforcement design and seismic safety evaluation of the concrete gravity dam, conventional linear-elastic response spectrum method cannot meet the requirement of engineering design. More and more experts and scholars realize that nonlinear FEM procedures are needed for the analysis of the behaviour of dams during strong earthquakes. The linear-elastic method cannot reflect the absorption of the earthquakes loading energy due to the plastic of concrete, the elastic stress may be higher than that of the real situation. It is not only unpractical, but also unnecessary that reinforces totally result from the static load and the analysis results of dynamic Code Spectrum. For the Xinfengjiang gravity dam, design earthquake load was reduced by old China Codes (NHCE 1978). That means the earthquake load effect after multiply 0.25 adds to the static load effect, then reinforced design was carried out according to the non-member system reinforced concrete structure. The dam is still running well after suffered its design earthquake (Huang 1989). It is enough to show that aseismic reinforcement design of the gravity dam according to this method is feasible. According to the seismic criterions of gravity dams, when suffering the rare earthquake, the dam’s crack is acceptable, as long as the dam meets the demands of bearing capacity, which means no dam-failure occurs (Lin 2001, Chen 2005). Now, the problem is that there is clear explain to the aseismic reinforcement design of gravity dam neither in the Seismic Design Code of Hydraulic Structures (DL5073-2000) (CIRWH 2000) nor in the Design Code for Hydraulic Concrete Structures (SL/T 191-96) (NHCE 1997) in China. In the former, there is just general statement of “should enhance the concrete strength or reinforced near the dam’s top” without specific aseismic reinforcement formula. In the latter, the reinforced method is not suitable for the concrete dam is pointed out. The design of aseismic reinforcement and the seismic safety evaluation for Jinanqiao roller compacted concrete (RCC) gravity dam are discussed in this paper. The RCC gravity dam is 160 meters high, and the dam site lies in the middle reaches of the Jinshajiang River in Yunnan province in China. The reinforced concrete nonlinear finite element time-history method is used to analyze the earthquake response of the dam. The strain rate, damage variable and stiffness degradation are included in the concrete elastic-plastic damage model. The ideal elastic-plastic constitutive relation is adopted in analysis. For the design of the steel reinforcement it is required that the crack does not damage the grout curtain in the dam heel, and cracks at the corners do not have any effect on the stability of the dam. Final amount of reinforcement is determined by the nonlinear earthquake response results of dam. The reinforcement scheme provides the basis for the design institute to determine the final reinforcement scheme. Aiming at the possible slip modes of the powerhouse dam section and the dam damage after considering the nonlinear earthquake response, aseismic stability evaluations of the dam are analyzed.