Seismic analysis of concrete gravity dams

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2019
Akpınar, Uğur
After the industrial revolution, energy has become one of the important issues determining the internal and external policies of the countries. Nowadays, to meet the energy needs of future generations and to reduce the damage to the environment, renewable energy sources are utilized. At this point, hydroelectric energy offers a clean and renewable energy source alternative. In addition to many built dams, the necessity of controlling existing dam stock punctuates the importance of studies on the seismic design and safety of concrete dams. In this study, the linear and nonlinear responses of concrete dams are evaluated and new simplified methods are proposed for the design and evaluation of the concrete dams. In the first part, linear response of concrete dams is examined. For this purpose, dynamic analyzes of a group of selected concrete dam sections were conducted. Analyses were carried out separately for the frequency domain where the dam-foundation-reservoir interactions can be accurately calculated and for the time domain where they can be calculated with approximate methods. By employing the results of the frequency domain solution, the tensile stresses in the heel, which is an important parameter in the design, were related to a number of engineering demand parameters. Additionally, effective damping ratios were obtained by comparing frequency and time domain solutions and a new damping ratio equation for time domain analysis was proposed. In the second part, nonlinear response of concrete dams is examined. The coupled solution of concrete nonlinearity and the dam-foundation-reservoir interaction is still a challenge for the current practices. For this purpose, a simplified static analysis method is proposed which can estimate the nonlinear damage of concrete dams including dam-reservoir interaction. In the method, the capacity curve was obtained by pushover analysis (including inertia and hydrodynamic effects) compatible with the first mode behavior. Such nonlinear problem can be a challenge to solve by the existing tools. For this purpose, the Sequential Linear Analysis (SLA) method was adopted to obtain the capacity curve. In order to verify the simplified static analysis method, nonlinear time domain analyzes were performed with selected sections and earthquake records. The damage was estimated by both techniques and compared to evaluate the performance of the simplified solution. Finally, the performance levels for concrete dams were estimated by using the results of nonlinear time domain analysis and deterministic sensitivity analysis. The resulting fragility curves and performance levels will be important tools to assist engineers in designing and evaluating concrete dams.