幼儿英语小故事 Reinforced Concrete
Plain concrete is formed from a harden数字英语ed mixture of cement ,water ,fine aggregate, coar aggregate (crushed stone or gravel),air, and often other admixtures. The plastic mix is placed and consolidated in the formwork, then cured to facilitate the acceleration of the chemical hydration reaction lf the cement/water mix, resulting in hardened concrete. The finished product has high compressive strength, and low resistance to tension, such that its tensile strength is approximately one tenth lf its compressive strength. Conquently, tensile and shear reinforcement in the tensile regions of ctions has to be provided to compensate for the weak tension regions in the reinforced concrete element.
It is this deviation in the composition of a reinforces concrete ction from the homogeneity of standard wood or steel ctions that requires a modified approach to the basic principles of structural design. The two components of the heterogeneous reinforced concrete ction are to be so arranged and proportioned that optimal u is made of the materials involved. This is possible becau concrete can easily be given any desired shape by placing and co
mpacting the wet mixture of the constituent ingredients are properly proportioned, the finished product becomes strong, durable, and, in combination with the reinforcing bars, adaptable for u as main members of any structural system.
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The techniques necessary for placing concrete depend on the type of member to be cast: that is, whether it is a column, a bean, a wall, a slab, a foundation. a mass columns, or an extension of previously placed and hardened concrete. For beams, columns, and walls, the forms should be well oiled after cleaning them, and the reinforcement should be cleared of rust and other harmful materials. In foundations, the earth should be compacted and thoroughly moistened to about 6 in. in depth to avoid absorption of the moisture prent in the wet concrete. Concrete should always be placed in horizontal layers which are compacted by means of high frequency power-driven vibrators of either the immersion or external type, as the ca requires, unless it is placed by pumping. It must be kept in mind, however, that over vibration can be harmful since it could cau gregation of the aggregate and bleeding of the concrete.
Hydration of the cement takes place in the prence of moisture at temperatures above 50°F. It is necessary to maintain such a condition in order that the chemical hydration reaction can take place. If drying is too rapid, surface cracking takes place. This would result in reduction of concrete strength due to cracking as well as the failure to attain full chemical hydration.
It is clear that a large number of parameters have to be dealt with in proportioning a reinforced concrete element, such as geometrical width, depth, area of reinforcement, steel strain, concrete strain, steel stress, and so on. Conquently, trial and adjustment is necessary in the choice of concrete ctions, with assumptions bad on conditions at site, availability of the constituent materials, particular demands of the owners, architectural and headroom requirements, the applicable codes, and environmental reinforced concrete is often a site-constructed composite, in contrast to the standard mill-fabricated beam and column ctions in steel structures.
A trial ction has to be chon for each critical location in a structural system. The trial s
ection has to be analyzed to determine if its nominal resisting strength is adequate to carry the applied factored load. Since more than one triagj是什么意思l is often necessary to arrive at the required ction, the first design input step generates into a ries of trial-and-adjustment analmhpyquality controls.
The trial-and –adjustment p乔布斯演讲中文字幕rocedures for the choice of a concrete ction lead to the convergence of analysis and design. Hence every design is an analysis once a trial ction is chon. The availability of handbooks, charts, and personal computers and programs supports this approach as a more efficient, compact, and speedy instructional method compared with the traditional approach of treating the analysis of reinforced concrete parately from pure design.
钢筋混凝土
素混凝土是由水泥、水、细骨料、粗骨料（碎石或卵石）、空气，通常还有
其他外加剂等经过凝固硬化而成。将可塑的混凝土拌合物注入到模板内，并将其世界贸易组织的英文缩写
捣实，然后进行养护，以加速水泥与水的水化反应，最后获得硬化的混凝土。其
最终制成品具有较高的抗压强度和较低的抗拉强度。其抗拉强度约为抗压强度的
十分之一。因此，截面的受拉区必须配置抗拉钢筋和抗剪钢筋以增加钢筋混凝土
构件中较弱的受拉区的强度
由于钢筋混凝土截面在均质性上与标准的木材或钢的截面存在着差异，因此，
需要对结构设计的基本原理进行修改。将钢筋混凝土这种非均质截面的两种组成
部分按一定比例适当布置，可以最好利用两种材料。这一要求是可以达到的。因
混凝土由配料搅拌成湿拌合物，经过振捣并凝固硬化，可以做成任何一种需要的
描写桂林山水的作文形状。如果拌制混凝土的各种材料配合比恰当，则混凝土制成品的强度较高，经
久耐用，配置钢筋后，可以作为任何结构体系的主要构件。
浇筑混凝土所需要的技术取决于即将浇筑的构件类型，诸如：柱、梁、墙、
板、基础，大体积混凝土水坝或者继续延长已浇筑完毕并且已经凝固的混凝土等
。对于梁、柱、墙等构件，当模板清理干净后应该其上涂油，钢筋表面的锈及其
他有害物质也应该被清除干净。浇筑基础前，应将坑底土夯实并用水浸湿6英寸，
以免土壤从新浇的混凝土中吸收水分。一般情况下。除使用混凝土泵浇筑外，混
凝土都应在水平方向分层浇筑，并使用插入式或表面式高频电动振捣器捣实。必
booby须记住过分的振捣将导致骨料离析和混凝土泌浆等现象，因而是有害的
水泥的水化作用发生在有水分存在，而且气温在50°F以上的条件下。为了保
证水泥的水化作用得以进行，必须具备上述条件。如果干燥过快则会出现表面裂
缝，这将有损于混凝土的强度，同时也会影响到水泥水化作用的充分进行。
设计钢筋混凝土构件时显然需要处理大量的参数，诸如宽度。、高度等几何
