1、2.1 Reinforced Concrete Plain concrete is formed from a hardened mixture of cement ,water ,fine aggregate, coarse 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
2、 hydration reaction If 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 If its compressive strength. Consequently, tensile and shear reinforcement in the
3、tensile regions of sections 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 section from the homogeneity of standard wood or steel sections that requires a modified approach to the basi
4、c principles of structural design. The two components of the heterogeneous reinforced concrete section are to be so arranged and proportioned that optimal use is made of the materials involved. This is possible because concrete can easily be given any desired shape by placing and compacting the wet
5、mixture of the constituent ingredients are properly proportioned, the finished product becomes strong, durable, and, in combination with the reinforcing bars, adaptable for use as main members of any structural system. The techniques necessary for placing concrete depend on the type of member to be
6、cast ,that is, whether it is a column, a beams, 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 harmf
7、ul materials. In foundations, the earth should be compacted and thoroughly moistened to about 6 in. in depth to avoid absorption of the moisture present in the wet concrete. Concrete should always be placed in horizontal layers which are compacted by means of high frequency power-driven vibrators of
8、 either the immersion or external type, as the case requires, unless it is placed by pumping. It must be kept in mind, however, that over vibration can be harmful since it could cause segregation of the aggregate and bleeding of the concrete. Hydration of the cement takes place in the presence of mo
9、isture at temperatures above 50F. 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
10、 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. Consequently, trial and adjustment is necessary in
11、 the choice of concrete sections, with assumptions based 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
12、contrast to the standard mill fabricated beam and column sections in steel structures. A trial section has to be chosen for each critical location in a structural system. The trial section has to be analyzed to determine if its nominal resisting strength is adequate to carry the applied factored loa
13、d. Since more than one trial is often necessary to arrive at the required section the first design input step generates into a series of trial and adjustment analyses. The trial and adjustment procedures for the choice of a concrete section lead to the convergence of analysis and design. Hence every
14、 design is an analysis once a trial section is chosen. 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 concret
15、e separately from pure design. 钢筋混凝土 普通混凝土是由水泥，水，细骨料，粗骨料（碎石或砾石），空气和其他一些经常用的外加剂等混合物构成。将混凝土放置在塑料模版内进行巩固，加速水化反应，使混凝土尽快硬化。混凝土的成品有较高的抗压强度，低导电性，它的抗拉强度约是抗压强度的十分之一。因此，在混凝土拉伸的时候，拉伸和剪应力加固在抗拉地区部分分配给补偿脆弱的地区。 正是因为这种偏差的存在，为了增强混凝土的抗压承载能力，我们根据实际需要对不同标准的木材或形钢的基本原理进行了结构设计，这两个钢筋混凝土异形截面构件受力情况是最合理的。我们可以将任何想要的形状通过压缩潮湿的混合
16、物形成正确匀称的比例，成品变的很坚固，耐用，结合混凝土内配筋情况，设计成各种受力合理的构建。 混凝土构建类型的不同导致所需的技术不同即 无论它是一列、梁、墙 ,一块 ,一个基金会。一个大规模的列 ,或 者一个扩展之前的放置和硬混凝 。对于墙，梁，柱来说表面的清洗应该非常灵活，在加固前应该及时清除铁锈和其他有害物质。在基金会上，地基应该夯实，排水，地下水不能影响到混凝土的。通过高频振动器的机动船根据实际需要将混凝土注入到水平层，但是震动会导致混凝土各层隔离或者水分溢出的现象。 温度高于 50F 的情况下水泥发生水化现象，我们需要保持这个状态方便化学水化反应的发生，如果干燥过快，会导致地面开裂。地
17、面开裂由于裂缝未能获得全化学水分，导致混凝土的强度降低。 很明显大量关于钢筋混凝土配合比的参数必须处理，如构件的几何 宽度，深度，面积加固，钢筋应变，混凝土应变，钢压力等等。因此，对具体部分进行试验和调整是非常必要的，基于现场条件进行假设，建筑和空间对组成材料的有特殊需求，相对于标准磨捏构造梁柱部分的钢结构，适用的法规和环境钢筋混凝土常常是一个站点构造的复合。 在结构体系中，试验部分已经被选为各个关键部分。试验部分必须进行分解，来确定实际受力是否足以承载力的极限。因为常常不只一个试验需要达到所需部分，所有第一个输入设计步骤生成一系列的试验和调整分析。 为混凝土部分选择的试验和调整过程引导出收敛性设计和分析。一旦试验部分被选 择那么每一相设计都是一种分析。手册、图表和与个人计算机和程序的用途支持这种方法作为一个更为高效的，紧凑、快速的教学方法与传统方法相比混凝土设计是比较简单的设计。
