Transient Analysis of Aged Concrete Damfoundation Coupled System
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Date
2011
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Abstract
The seismic behavior of concrete dams has been the subject of extensive research during the past decades because of concern for dam safety during earthquakes. Concrete dams are distinguished from other structures because of their huge size and their interactions with the adjacent reservoir and underlying foundation. The safety evaluation of the concrete gravity dams subjected to severe seismic excitations is really very complex as they create coupling effect with the underlying foundation. The interaction among dam, reservoir and its foundation may alter the actual behavior of the dam considerably than what is obtained from the consideration of the dam alone. Therefore, it is necessary to take into account the coupled dam-foundation-reservoir interaction effects for the sound design of the concrete dam. While the structural models are relatively simpler, foundation models are often complicated due to their unbounded nature and nonlinear stress-strain characteristics. Because of nonlinear stress-strain behavior of soil/rock material, it is important to consider its effect while carrying out soil-structure interaction analysis. An attempt is made here to develop a method to assess the effect of soil-structure interaction on the seismic response of dam to make its design more realistic. Due to ageing, the dams are subjected to severe environmental effects, which may lead to loss of stiffness as well as strength due to material degradation. Since the dam face is in constant contact with water, concrete degradation due to hygro-mechanical loading is inevitable and should be considered in the analysis procedure. This ageing process of concrete leads to loss of stiffness and strength of the material. Therefore, to assess the behavior of the dam at a later stage of its life, it is important to determine the proper strength of the concrete at a certain age. An approach to include the time dependent degradation of concrete owing to various environmental factors is presented. Both the aged dam and foundation domains are analyzed separately with the interaction effects at the dam-foundation interface enforced by a developed iterative scheme. In the present work, an appropriate method is presented to truncate infinite foundation domain with absorbing dampers. The finite element method is used to model both dam and foundation. The results obtained from present dam-foundation interaction analyses presents the trends to be expected for a concrete gravity dam at a later stage after construction which may help a designer in the decision making process..
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Supervisor: S Sreedeep
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CIVIL ENGINEERING