UNIT 3 reinforced concrete

1、Although concrete is used very extensive in the construction of buildings, bridges and many other engineering structures, its mechanical properties are far from ideal. For example, it is not a particularly strong material. 雖然混凝土已廣泛應(yīng)用于房屋建筑、橋梁和其他許多工程結(jié)構(gòu)物中，但它的力學(xué)性能卻很不理想。例如，它的強(qiáng)度不是很高。The tensile strength o

2、f concrete is extremely low, about one-tenth of its compressive strength and this precludes the use of plain concrete for most structural members. 混凝土的抗拉強(qiáng)度非常低，大約是抗壓強(qiáng)度的1/10，因此大多數(shù)結(jié)構(gòu)構(gòu)件不能用素混凝土制作。The elastic modulus for concrete subjected to compressive stress of short duration is reasonably high, in the

3、 range of 20,000 to 30,000 Mpa (about one-tenth of the elastic modulus of steel);混凝土短期受壓時(shí)的彈性模量相當(dāng)高，為2000030000Mpa（大約是鋼彈性模量的1/10）；however, concrete undergoes large additional long-term deformations due to creep and shrinkage, so that the effective stiffness is much lowerperhaps a third to a quarter of

4、 the instantaneous stiffness.然而由于徐變和收縮，混凝土在又會(huì)產(chǎn)生較大的長(zhǎng)期變形，所以其有效剛度要低得多可能只有瞬時(shí)剛度的1/3到1/4。The widespread use of concrete in engineering construction stems from its cheapness compared with other structural materials currently available.混凝土在工程建筑中能得到廣泛應(yīng)用，是因?yàn)樗饶壳俺Ｓ玫钠渌ㄖ牧媳阋?。Its lack of tensile strength is over

5、come by including reinforcement, usually in the form of steel bars, to produce a composite material known as reinforced concrete.其抗拉強(qiáng)度低的缺點(diǎn)則用加配鋼筋以形成稱為鋼筋混凝土的復(fù)合材料來(lái)克服。Although the steel reinforcement does not prevent cracking of the concrete in regions of tension, it does prevent the cracks from widenin

6、g, and it provides an effective means for resisting the internal tensile forces.雖然鋼筋不能防止混凝土受拉區(qū)裂縫的產(chǎn)生，但是確實(shí)能限制裂縫的開(kāi)展，因此提供了抵抗內(nèi)拉力的有效手段。The quantity of reinforcement need is usually quite small, relative to the volume of concrete, so that the total cost of reinforced concrete construction remains commercia

7、lly very competitive.所需鋼筋的數(shù)量，與混凝土的體積相比往往是很小的，所以鋼筋混凝土結(jié)構(gòu)的總造價(jià)在市場(chǎng)上的競(jìng)爭(zhēng)力仍很強(qiáng)。The primary purpose of the steel reinforcement is to carry internal tensile forces. Reinforcement is therefore placed in beams near the tensile face, i.e., near the lower face in the in-span regions of positive moment and near the

8、 upper face in regions near internal supports, where negative moments act. This is illustrated in Fig.6.1.鋼筋的主要用途是承受內(nèi)拉力，因此鋼筋要放在梁內(nèi)靠近受拉面，即在跨中正彎矩區(qū)靠近下面，而在內(nèi)支座負(fù)彎矩區(qū)靠近上面，如圖6.1所示。In reinforced concrete design, it is important to provide reinforcement in all regions of potential cracking.在鋼筋混凝土結(jié)構(gòu)設(shè)計(jì)中，要在所有可能出現(xiàn)裂

9、縫的區(qū)域都放置鋼筋，這一點(diǎn)很重要。Thus a rectangular arrangement of vertical and horizontal steel bars is introduced into regions of a beam where inclined cracks can form as a result of combined shearing action and bending moment.因而在由于剪切和彎曲聯(lián)合作用而使梁產(chǎn)生斜裂縫的區(qū)域要放置成矩形配置的垂直和水平鋼筋。 The longitudinal steel, or main reinforcemen

10、t, and the transverse bars, called stirrups, may be preassembled into a reinforcing cage for ease of construction.為了便于施工，縱向鋼筋（主筋）和橫向鋼筋（箍筋）可以預(yù)先綁扎成鋼筋骨架。In a floor slab, bars are usually laid in the two main span directions at right angles, to resist the tensile forces produced by the bending actions i

11、n each direction. For ease of construction, welded mesh is frequently used as slab reinforcement.在樓板中，鋼筋往往是沿著兩個(gè)主跨方向成直角配置，以抵抗每一方向由于受彎而產(chǎn)生的拉應(yīng)力。為了便于施工，板筋常常采用焊接鋼筋網(wǎng)。Although steel reinforcement is used primarily to carry the internal tensile forces produced by external loading, it also has other uses.雖然鋼筋

12、主要用來(lái)承受由外荷載產(chǎn)生的內(nèi)拉力，但它還有別的用途。Steel is much stronger than concrete in compression and it is sometimes used to boost the resistance of zones of compression, when the overall dimensions of the member are restricted.鋼筋承受壓力的能力比混凝土強(qiáng)得多，所以當(dāng)構(gòu)件的總尺寸受限制時(shí)，有時(shí)也用鋼筋來(lái)加強(qiáng)受壓區(qū)的抵抗能力。Longitudinal steel is placed in all compre

13、ssion members. In such members, bending is usually present in addition to axial compression and the longitudinal steel reinforcement at each face of the member may act either in tension or compression.這時(shí)在所有受壓構(gòu)件中都放置縱向鋼筋，這樣的構(gòu)件除承受軸向壓力外往往還受彎，這時(shí)配置在構(gòu)件每一面的縱向鋼筋或是受拉，或是受壓。Transverse ties are used to maintain

14、the longitudinal steel in position during casting of the concrete and later to prevent its outward buckling when it is subjected to compressive stress. Again, the reinforcing steel for the column may be preassembled into a cage.橫向鋼筋用來(lái)在澆筑混凝土?xí)r保持縱向鋼筋的位置，以后當(dāng)鋼筋承受壓力時(shí)，則用來(lái)放置鋼筋向外屈曲。同樣，柱子的鋼筋也可預(yù)先綁扎成骨架。Cracking

15、 in concrete may be caused not only by external loading, but also by temperature gradients and differential or restrained shrinkage. 不僅是由于外荷載，而且也由于溫差以及不均勻收縮或收縮受阻，混凝土都會(huì)開(kāi)裂。Secondary reinforcement is therefore provided to control such cracking, which may be unsightly and even dangerous.因而要配置輔助鋼筋以控制這樣的裂

16、縫，這些裂縫可能很難看，甚至?xí)l(fā)生危險(xiǎn)。Plain concrete is formed from a hardened mixture of cement, water, fine aggregate, coarse aggregate (crushed stone or gravel), air, and often other admixtures. 素混凝土是一種由水泥、水、細(xì)骨料、粗骨料（碎石或礫石），空氣，通常還有外加劑構(gòu)成的一種硬化混合物。The plastic mix is placed and consolidated in the form-work, then cured

17、 to facilitate the acceleration of the chemical hydration reaction of the cement/water mix, resulting in hardened concrete. 塑性混合料在澆筑模板時(shí)添加，接下來(lái)進(jìn)行養(yǎng)護(hù)促進(jìn)水泥和水拌合后的水化反應(yīng)的速度，使混凝土硬化。The finished product has high compressive strength, and low resistance to tension, such that its tensile strength is approximately

18、 one-tenth of its compressive strength. 制作完成的構(gòu)件有較高的抗壓強(qiáng)度以及較低的抗拉強(qiáng)度，其抗拉強(qiáng)度大約為抗壓強(qiáng)度的十分之一。Consequently, tensile and shear reinforcement in the tensile regions of sections has to be provided to compensate for the weak-tension regions in the reinforced concrete element.因此，在鋼筋混凝土構(gòu)件中，受拉區(qū)的抗拉和抗剪鋼筋不得不為弱受拉區(qū)/弱張力區(qū)提供

19、補(bǔ)償。It is this deviation in the composition of a reinforced concrete section from the homogeneity of standard wood or steel sections that requires a modified approach to the basic principles of structural design.正是由于鋼筋混凝土構(gòu)件的組成成分的這種偏差，從標(biāo)準(zhǔn)的木材或鋼筋部分的均一性來(lái)說(shuō)，需要進(jìn)行改良以符合結(jié)構(gòu)設(shè)計(jì)的基本原則。The two components of the hete

20、rogeneous reinforced concrete section are to be so arranged and proportioned that optimal use is made of the materials involved.不均一鋼筋混凝土構(gòu)件的兩個(gè)組成部分要合理安排和配比以實(shí)現(xiàn)組成材料的最優(yōu)利用。This is possible because concrete can easily be given any desired shape by placing and compacting the wet mixture of the constituent i

21、ngredients into suitable forms in which the plastic mass hardens.這很可能是由于混凝土材料能夠輕易地形成任何想要得到的形狀，在大體積混凝土硬化的過(guò)程當(dāng)中將組成材料的含水拌合物澆筑和壓實(shí)成合適的形狀。If the various ingredients are properly proportioned, the finished product becomes strong, durable, and, in combination with the reinforcing bars, adaptable for use as m

22、ain members of any structural system.如果各種原料/成分比例恰當(dāng)，成品就強(qiáng)度足夠并且耐久性好，配置鋼筋后可用作任何結(jié)構(gòu)體系的主要構(gòu)件。The techniques necessary for placing concrete depend on the type of member to the cast: that is, whether it is a column, a beam, a wall, a slab, a foundation, a mass concrete dam, or an extension of previously place

23、d and hardened concrete.澆筑混凝土所需的技術(shù)取決于澆鑄構(gòu)件的類型，也就是說(shuō)，不管是一個(gè)柱子、一根梁、一面墻、一塊板、一個(gè)基礎(chǔ)、一塊大體積混凝土或先前澆筑好且已硬化的混凝土的延伸/擴(kuò)大。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. 對(duì)于梁、柱、墻在清洗之后應(yīng)該涂油放水，鋼筋表面的鐵銹和其他有害的材料應(yīng)該

24、被清除。In foundations, the earth should be compacted and thoroughly moistened to about 6in. in depth to avoid absorption of the moisture present in the wet concrete.在基礎(chǔ)當(dāng)中，地基土應(yīng)該被壓實(shí)和徹底浸濕大約6英寸的深度，以防地基土吸收濕混凝土當(dāng)中的水分。Concrete should always be placed in horizontal layers, which are compacted by means of high-f

25、requency power-driven vibrators of either the immersion or external type, as the case requires, unless it is placed by pumping.混凝土總是在水平層進(jìn)行澆注，通過(guò)電力驅(qū)動(dòng)的高頻振動(dòng)碾進(jìn)行壓實(shí)，深入內(nèi)部或在表面進(jìn)行壓實(shí)，除了特殊情況下，一般都是用泵送混凝土進(jìn)行澆注。It must be kept in mind, however, that over-vibration can be harmful since it could cause segregation of t

26、he aggregate and bleeding of the concrete.然而，值得注意的是，過(guò)度的振動(dòng)會(huì)導(dǎo)致骨料的分離和混凝土漿液的流出。Hydration of the cements takes place in the pressure of moisture at temperatures above 50F.水泥水化發(fā)生在溫度超過(guò)50華氏溫度下的水分的壓力。It is necessary to maintain such a condition in order that the chemical hydration reaction can take place.為了化

27、學(xué)水化反應(yīng)的產(chǎn)生，維持這樣一個(gè)條件是很必要的。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.如果干燥過(guò)快會(huì)導(dǎo)致表面開(kāi)裂。開(kāi)裂會(huì)導(dǎo)致混凝土強(qiáng)度的降低和化學(xué)水化反應(yīng)的不足。It is clear that a large number of parameters have to be deal

28、t with in proportioning a reinforced concrete element, such as geometrical width, depth, area of reinforcement, steel strain, concrete strain, steel stress, and so on.顯然，鋼筋混凝土配比過(guò)程需要大量的系數(shù)，如，幾何寬度、高度，鋼筋面積，鋼筋應(yīng)變，混凝土應(yīng)變，鋼筋應(yīng)力等等。Consequently, trial and adjustment is necessary in the choice of concrete sectio

29、ns, with assumptions based on conditions at site, availability of the constituent materials, particular demands of owners, architectural and headroom requirements, the applicable codes, and environmental conditions.因此，在選擇混凝土構(gòu)件上進(jìn)行的試驗(yàn)和調(diào)整是非常必要的，根據(jù)壩址情況的假定，材料成分的可利用性，特別是業(yè)主的要求，建筑學(xué)的和凈空高度的需求，適用的規(guī)范以及環(huán)境條件。Such

30、 an array of parameters has to be considered because of the fact that the reinforced concrete is often a site-constructed composite, in contrast to the standard mill-fabricated beam and column sections in steel structures.這樣的一個(gè)數(shù)組的參數(shù)是必須考慮的，因?yàn)閷?shí)際上鋼筋混凝土往往是現(xiàn)場(chǎng)復(fù)合材料構(gòu)建的，和標(biāo)準(zhǔn)裝配的梁以及柱構(gòu)件的鋼結(jié)構(gòu)進(jìn)行對(duì)比。A trial section has to be chosen for each critical location