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A gravity dam is a dam constructed from concrete or stone masonry and designed to hold back water by utilizing the weight of the material alone to resist the horizontal pressure of water pushing against it. Gravity dams are designed so that each section of the dam is stable, independent of any other dam section.〔( Design of Gravity Dams, Bureau of Reclamation, 1976 )〕〔( Design of Small Dams, Bureau of Reclamation, 2004 )〕 The most common classification of gravity dams is by the materials composing the structure: * Concrete dams include * * mass concrete dams, made of: * * * conventional concrete: Dworshak Dam, Grand Coulee Dam * * * roller-compacted concrete: Willow Creek Dam (Oregon), Upper Stillwater Dam * * masonry: Pathfinder Dam, Cheesman Dam * * hollow gravity dams, made of reinforced concrete: Braddock Dam Composite dams are a combination of concrete and embankment dams. Construction materials of composite dams are the same used for concrete and embankment dams. Gravity dams can be classified by plan (shape): * Most gravity dams are straight (Grand Coulee Dam). * Some masonry and concrete gravity dams have the dam axis curved (Shasta Dam, Cheesman Dam) to add stability through arch action.〔(Gravity Dam Design, US Army Corps of Engineers, EM 1110-2-2200, June 1995 )〕 Gravity dams can be classified with respect to their structural height: * Low, up to 100 feet. * Medium high, between 100 and 300 feet. * High, over 300 feet. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gravity dam」の詳細全文を読む スポンサード リンク
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