The Study On The Non-uniform Ground Motion Input And Seismic Mechanism Of Shapai Arch Dam

A large number of high arch dams are being constructed in the western region ofChina, many of these dams are higher than200m, and located in earthquake proneareas. The seismic safety of these dams is directly related to the lives and property ofdownstream residents, so the research on the seismic mechanism of high arch dams haslong been a hot issue. In the seismic input mechanism of arch dam, it is still a commondesign to use thetruncated foundation boundary and consider the ground motionin uniform amplitude and phase.But plenty of measured data have shown that,there is a significant non-uniformity for the ground motion along the damfoundation surface for super-large structures such as arch dam, due to travellingwave effects, local site effects and partial coherence effects. Thisnon-uniformity still lacks of systematic research.This thesis is divided into three parts. The first part aims to study on the effects ofthe canyon to this non-uniformity, and analyze the affecting factors. To discuss theinfluence of the width of the canyon, the depth of the canyon, the shape of the canyon,the orientation of the seismic source and the frequency of the wavelet on thedisplacement and acceleration of the canyon surface, this paper simulates the wave fieldusing finite difference method, with boundary-conforming grid to solve the issue ofsurface topography.The second part discusses the seismic mechanism of the Shapai arch damunder beyond-design seismic loading. First, we calculate the linear elastic,massless foundation model, whose results show a big arch tensile stress on thedam, inevitably resulting in the opening of the contraction joints. Therefore, weconsider the effects of the contraction joints with dynamic contact method, inwhich the arch tensile stress is significantly decreased, while the cantilevertensile stress on the downstream face is increased. To simulate the mechanismof energy radiation to infinity, we further add the viscous boundary to the model.Finally, we change the seismic input into the measured seismogram ofWenchuan earthquake near Shapai instead of the artificial earthquake generatedfrom the spectrum in the code, and take the material non-linearity into consideration. The results show severe damage on the elevation of1830mof thedownstream face. The position and the shape of the cracks calculated withnumerical simulation are consistent with the real situation of the Shapai archdam.The final part combines the first two parts, in order to discuss the effects ofthe non-uniform input of amplitude and phase to the Shapai arch dam. Thecalculation demonstrates that the non-uniform inputhas an impact both onthemaximum stress and the stress distribution of the dam. However, therelationship is rather complex, and further study is needed.