Thermal cracking of a concrete arch dam due to seasonal temperature variations

University essay from KTH/Betongbyggnad

Abstract: Concrete dams located in northern regions are exposed to large seasonal temperature variations. These seasonal temperature variations have resulted in cracking in thin concrete dams. Continuous monitoring and evaluation of existing dams are important to increase the knowledge about massive concrete structures and to ensure dam safety.  The aim of this degree project is to increase the knowledge about how cracking occurs in concrete dams and how it affects the dam safety. This was achieved by simulating the development of cracks in a concrete arch dam exposed to seasonal temperature variations using finite element analysis (FEA). The accuracy of the model was evaluated by comparing the results with measurements from a Swedish concrete arch dam. Finally, effect of cracks and temperature on the dam safety was investigated.  FEA was used to predict the crack pattern and displacements in the arch dam. The analyses were performed both with linear elastic and nonlinear material behavior. Two models were analyzed, in one model the dam was considered to be a homogeneous arch, the other model included contraction joints. The cracking was simulated using temperature envelopes from the location of the Swedish arch dam. To evaluate the displacements in the arch, further analyses were carried out, where the cracked arch dam was exposed to the actual temperature variations at the location. The results were compared to the crack pattern and measurements of displacements of the Swedish arch dam. To investigate the effects from the cracking on the safety of the dam, a progressive failure analyses performed.  The results show that the downstream face of the arch cracked under hydrostatic pressure. The cracks propagated further during winter when the temperature load was applied. The resulting crack pattern corresponded well with the survey of the cracks from the Swedish arch dam. The FE-models with nonlinear material developed a horizontal plastic hinge due to excessive cracking in a region halfway down from the crest. The plastic hinge affected the shape of the deflected arch. The magnitude of the displacements and the shape of the deflected arch was captured with the nonlinear models. A safety factor of 3 for internal structural failure in the arch was found in the failure analyses. The safety factor of the arch only decreased slightly due to the cracking. During a cold winter, the safety factor decreased to 2.5.

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