Design
Arch dams require a high level of stress and force analysis in order to create a sufficient design. The main force against an arch dam is the hydrostatic pressure provided by the reservoir behind it, uplift, which is water pressure beneath the dam, the weight of the dam itself, and all the forces combined. Other forces that affect a dam include, but are not limited to, temperature, chemical reactions, settling, silt accumulation, and earthquakes.
Most often, the arch dam is made of concrete and placed in a "V"-shaped valley. The foundation or abutments for an arch dam must be very stable and proportionate to the concrete. There are two basic designs for an arch dam: constant-radius dams, which have constant radius of curvature, and variable-radius dams, which have both upstream and downstream curves that systematically decrease in radius below the crest. A dam that is double-curved in both its horizontal and vertical planes may be called a dome dam. Arch dams with more than one contiguous arch or plane are described as multiple-arch dams. Early examples include the Roman Esparragalejo Dam with later examples such as the Daniel-Johnson Dam (1968) and Itaipu Dam (1982). At an increased cost, an arch dam can have steel rods or pre-stressed steel cable reinforcements and therefore require less concrete than does a gravity dam or arch-gravity dam. As arch dams are commonly constructed in remote mountainous areas, less material is beneficial when it has to be delivered with difficulty to the site. However, as a result of the failure of the Gleno Dam shortly after it was constructed in 1923, the construction of new multiple arch dams has become less popular.
In general, arch dams are classified as thin, medium, or thick. If width of an arch dam's base is 2/10 of the dam's height or less, it is thin. Any base and height ratio greater than 2/10 but less than 3/10 is considered medium. Thick is a ratio of 3/10 or greater. In addition, an arch dam's base is historically just as thick as the crest, but often it is twice as thick as the crest. Contraction joints are normally placed every 20 m in the arch dam and are later filled with grout after the control cools and cures.
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