Abstract—Alkali-Aggregate Reaction (AAR) is one of the phenomena that during the life time of concrete, endangers it, and is one of the factors that cause serious damages to wet concrete structures, such as concrete dams. The most important structural effect of this reaction is the creation of strain in concrete due to expansion of concrete. In this paper, in order to evaluate the effect of AAR, one of the gravity dams at Beauharnois power plant, which showed signs of this reaction, was studied, and a software program based on finite element was used. In this paper, the dam is analyzed assuming that AAR does not occur. Then the dam with the case that is analyzed considering this reaction, the results were evaluated and compared. This comparison shows a big difference between the results of the two conditions, and that expresses the substantial effect of AAR on the dam. Displacements are some of these effects.