土木专业外文翻译3-建筑结构(编辑修改稿)

土木专业外文翻译3-建筑结构(编辑修改稿)内容摘要：

ughout the structure. Problems of materials. Each of the two basic dam materials, concrete and earth or rock fill, has a weakness that must be overe by the proper design of the dam. Weaknesses of concrete.. Concrete is weak in tensile strength。 that is, it can be pulled apart 2 easily. Concrete dams must therefore be designed to place minimum tensile strain on the dam and to make use of concrete’s great pressive strength, or ability to support vertical loads. The chief constituent of concrete, cement, shrinks as it sets and hardens, due to water absorption in the crystalline structure, to evaporation of water to the atmosphere, and to cooling form the higher temperatures reached when the chemical reactions in the cement are in progress during hydration. Because of the large volume of concrete in a dam, shrinkage presents a serious cracking hazard. Various expedients are used to overe the problem. Concrete is usually cast in separate blocks of limited height. Gaps may be left to permit heat losses and filled in later. Lowheat cements may be used。 these are specially blended so that rates of heat evolution are retarded. Cement content can be safely reduced in the interior concrete in the dam, in which strength and resistance to climatic and chemical deterioration are less important. The cement content, and therefore the heat caused by hydrating, can also be reduced by using aggregate (the other major constituent of concrete) of larger stones. Another expedient is to use other finegrained materials, such as fly ash (pulverized fuel), as filler, reducing the total cement volume in the concrete. Another is to use certain additives, surfaceactive agents, and airentraining agents that permit using a lower watertocement ratio in mix by ice, circulating water through pipes laid in the concrete, and extracting excess water from surfaces by vacuum. Weaknesses of earth and rock fill. Soils and rock fragments lack the strength of concrete, are much more permeable, and possess less resistance to deterioration and disturbance by flowing water. These disadvantages are pensated for by a much lower cost and by the ability of earth fill to adapt to deforma。