| The power station at dam toe is widely applied at home and abroad. There is a permanent joint between dam and powerhouse at dam toe, but in recent years replacing conventional expansion joint by penstock with cushion layer is more and more common in actual projects. In condition of penstock with cushion layer, continuous penstock and joint grouting provide load paths for interaction between powerhouse and dam. From the view of powerhouse, penstock is directly connected with the key spiral case, so the effect of powerhouse and dam interaction on the mechanical properties of spiral case structure deserves attention. Furthermore, with a frequent seismic activity in southwest China, high attention has been given to the earthquake-resistance of powerhouse structure. For powerhouse at dam toe, there are some problems deserved further study, such as powerhouse and foundation dynamic interaction, powerhouse and adjacent dam dynamic interaction, failure mode of powerhouse in rare earthquake. On account of the aforementioned problems, by means of the finite element method, this dissertation is restricted to the discussion of the following aspects based on some case studies.(1) In order to reveal the effect of powerhouse and dam interaction on the stable operation of hydroelectric generating unit, based on the whole FEM model of powerhouse, dam and foundation, effect of time to shutting penstock preparatory circumferential welding seam and grouting joint on structural characteristics of spiral case with a membrane was studied quantitatively. The result shows that thrust forces transfered by penstock and grouting are bigger when shutting preparatory circumferential welding seam at lower water level, but Mises stress of spiral case is affected slightly by the thrust forces. Anti-thrust ring can resist the thrust force transfered by penstock effectively and is favorable for shear strength of stay ring and stability of spiral case with a membrane. On the other side, the thrust force transfered by joint grouting can decrease generator pedestal’s nonuniform deformation caused by downstream water pressure, so shutting preparatory circumferential welding seam and grouting joint at low water level was suggested to guarantee safe and stable operation of hydroelectric generating unit.(2) In order to analyze the contact behavior of preloading filling spiral case for powerhouse at dam toe, considering different connecting forms of inlet structure, the mechanical properties from construction period to operating period were studied using a new simulation method which is based on joint and contact elements. Simplified mehtod’s error was also analyzed. The result shows that global deformation caused by spiral case’s unbalanced thrust and the thrust transfered by penstock is a key factor for closing characteristic of preloading gap. Due to global deformation, the earliest closed region locates at the outside of inlet section,45° section and the inside of 270° section where are opposite to the unclosed region when the inner pressure reaches the preloading head. Anti-thrust ring can effectively resist the unbalanced thrust and transfered thrust and is favorable for preloading gap’s uniform closing. The stress state of surrounding concrete and simplified mehtod’s error are both closely related to connecting forms of inlet structure. Considering the unsafe error to projects, using simulation method for reinforcement calculation was recommended. In stay ring’s design, shear resistance and torsion resistance should be paid more attention, adding anti-thrust ring is favorable for stay ring’s stability.(3) For seismic analysis of powerhouse at dam toe, treatment modes of foundation and dam are two important problems for final results. The difference among rigid foundation, mass-less foundation and infinite foundation was firstly studied using dynamic time history method, then the effect of powerhouse and dam interaction on powerhouse’s seismic response was studied based on infinite foundation. The result shows that there is no exact magnitude relation between rigid foundation and mass-less foundation, calculation results of above two foundations are both bigger than that of infinite foundation. The reason for mass-less foundation is radiation damping while the relation between rigid foundation and infinite foundation deserves more research efforts. For powerhouse’s seismic design, the combination of rigid foundation and infinite foundation was recommended, only using mass-less foundation to guide practical projects is not reasonable. Powerhouse and dam interaction transfered by foundation and joint grouting can both decrease powerhouse’s seismic response, so only modeling powerhouse and setting free boundary on upstream surface is conservative and safe for powerhouse’s seismic design.(4) Based on extensive reading of research findings in terms of performance-based seismic design, making efforts to put forward the performance objectives from five aspects for hydropower house. Then applicability of concrete damage plastic model in ABAQUS for repeated cyclic loading condition was verified, test result shows that this model can simulate combined damage behavior under tension and compression and stiffness conversion behavior. Based on above works, nonlinear dynamic time history analysis under three level earthquake action of an actual powerhouse at dam toe was carried out to study its failure mode and seismic performance. The result shows that in rare earthquake action, damage degree from serious to slight is severe cracks in downstream column, cracks in upstream column, cracks in upstream wall and compressive damage in downstream column. Damage degree in frequent and design earthquake action is far lower than that in rare earthquake action. In each level earthquake action powerhouse’s seismic performance can meet the suggested performance objectives and shows high safe capacity. But there is collapse risk for roof net in rare earthquake action, the high dynamic stress of roof net is caused by upstream and downstream walls’unconsistency motion. This phenomenon and roof net’s seismic design should be paid more attention. |
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