Cracking and failure of hydroelectric engineering structures due to thermal loads

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Zhang, Pixin
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Many hydraulic structures exhibit significant cracking, which allows water intrusion into or through the structures. These cracks are the result of a variety of phenomena, including thermal gradient, ice loading, restrained concrete shrinkage and cycles of freezing and thawing. Conventional repair methods generally consist of local sealing of cracks and defective construction joints by cementitious or chemical grouting. In many cases, such repair is effective only for a few years and additional measures are required. The study of the mechanism of structural failures and repair effects is very meaningful for the rehabilitation of hydraulic structures. This thesis is devoted to the analyses of dams with cracked construction joints. Such structural failure may result from the destructive combination of harsh weather conditions and ice loads. Existing methods for transient temperature analysis of dams are first discussed and suggestions are made on the suitable choice of the initial and boundary conditions for the design of new dams and rehabilitation of cracked dams. The motion of dams with defective construction joints is analyzed as a contact problem. A highly accurate interface stress evaluation method is presented for the development of an effective algorithm of crack or joint open and close displacement analysis. The results of field measurement and theoretical analyses of ice formation, horizontal and vertical loads on structures are summarized. Practical ice loading models are established in terms of ambient temperature and other environment conditions. The dam motion, especially the joint open-close displacement is umerically simulated. The results are calibrated through field measurements. The influence of the thermal and ice loads on the dam motion are studied. The mechanism of construction joint failure is clearly captured through the interface stress analysis results. Important conclusions are drawn for both repair work and anchor strengthening strategies.