土木工程――鋼筋混凝土外文翻譯

1、Reinforced ConcreteConcrete and reinforced concrete are used as building materials in every country. In many, including the United States and Canada, reinforced concrete is a dominant structural material in engineered construction. The universal nature of reinforced concrete construction stems from

2、the wide availability of reinforcing bars and the constituents of concrete, gravel, sand, and cement, the relatively simple skills required in concrete construction, and the economy of reinforced concrete compared to other forms of construction. Concrete and reinforced concrete are used in bridges,

3、buildings of all sorts underground structures, water tanks, television towers, offshore oil exploration and production structures, dams, and even in ships.Reinforced concrete structures may be cast-in-place concrete, constructed in their final location, or they may be precast concrete produced in a

4、factory and erected at the construction site. Concrete structures may be severe and functional in design, or the shape and layout and be whimsical and artistic. Few other building materials off the architect and engineer such versatility and scope.Concrete is strong in compression but weak in tensio

5、n. As a result, cracks develop whenever loads, or restrained shrinkage of temperature changes, give rise to tensile stresses in excess of the tensile strength of the concrete. In a plain concrete beam, the moments about the neutral axis due to applied loads are resisted by an internal tension-compre

6、ssion couple involving tension in the concrete. Such a beam fails very suddenly and completely when the first crack forms. In a reinforced concrete beam, steel bars are embedded in the concrete in such a way that the tension forces needed for moment equilibrium after the concrete cracks can be devel

7、oped in the bars.The construction of a reinforced concrete member involves building a from of mold in the shape of the member being built. The form must be strong enough to support both the weight and hydrostatic pressure of the wet concrete, and any forces applied to it by workers, concrete buggies

8、, wind, and so on. The reinforcement is placed in this form and held in place during the concreting operation. After the concrete has hardened, the forms are removed. As the forms are removed, props of shores are installed to support the weight of the concrete until it has reached sufficient strengt

9、h to support the loads by itself.The designer must proportion a concrete member for adequate strength to resist the loads and adequate stiffness to prevent excessive deflections. In beam must be proportioned so that it can be constructed. For example, the reinforcement must be detailed so that it ca

10、n be assembled in the field, and since the concrete is placed in the form after the reinforcement is in place, the concrete must be able to flow around, between, and past the reinforcement to fill all parts of the form completely.The choice of whether a structure should be built of concrete, steel,

11、masonry, or timber depends on the availability of materials and on a number of value decisions.The choice of structural system is made by the architect of engineer early in the design, based on the following considerations:1. Economy. Frequently, the foremost consideration is the overall const of th

12、e structure. This is, of course, a function of the costs of the materials and the labor necessary to erect them. Frequently, however, the overall cost is affected as much or more by the overall construction time since the contractor and owner must borrow or otherwise allocate money to carry out the

13、construction and will not receive a return on this investment until the building is ready for occupancy. In a typical large apartment of commercial project, the cost of construction financing will be a significant fraction of the total cost. As a result, financial savings due to rapid construction m

14、ay more than offset increased material costs. For this reason, any measures the designer can take to standardize the design and forming will generally pay off in reduced overall costs.In many cases the long-term economy of the structure may be more important than the first cost. As a result, mainten

15、ance and durability are important consideration.2. Suitability of material for architectural and structural function.A reinforced concrete system frequently allows the designer to combine the architectural and structural functions. Concrete has the advantage that it is placed in a plastic condition

16、and is given the desired shape and texture by means of the forms and the finishing techniques. This allows such elements ad flat plates or other types of slabs to serve as load-bearing elements while providing the finished floor and / or ceiling surfaces. Similarly, reinforced concrete walls can pro

17、vide architecturally attractive surfaces in addition to having the ability to resist gravity, wind, or seismic loads. Finally, the choice of size of shape is governed by the designer and not by the availability of standard manufactured members.3. Fire resistance. The structure in a building must wit

18、hstand the effects of a fire and remain standing while the building is evacuated and the fire is extinguished. A concrete building inherently has a 1- to 3-hour fire rating without special fireproofing or other details. Structural steel or timber buildings must be fireproofed to attain similar fire

19、ratings.4. Low maintenance. Concrete members inherently require less maintenance than do structural steel or timber members. This is particularly true if dense, air-entrained concrete has been used for surfaces exposed to the atmosphere, and if care has been taken in the design to provide adequate d

20、rainage off and away from the structure. Special precautions must be taken for concrete exposed to salts such as deicing chemicals.5. Availability of materials. Sand, gravel, cement, and concrete mixing facilities are very widely available, and reinforcing steel can be transported to most job sites

21、more easily than can structural steel. As a result, reinforced concrete is frequently used in remote areas.On the other hand, there are a number of factors that may cause one to select amaterial other than reinforced concrete. These include:1. Low tensile strength. The tensile strength concrete is m

22、uch lower than its compressive strength ( about 1/10 , and hence concrete is subject to cracking. In structural uses this is overcome by using reinforcement to carry tensile forces and limit crack widths to within acceptable values. Unless care is taken in design and construction, however, these cra

23、cks may be unsightly or may allow penetration of water. When this occurs, water or chemicals such as road deicing salts may cause deterioration or staining of the concrete. Special design details are required in such cases. In the case of water-retaining structures, special details and / of prestres

24、sing are required to prevent leakage.2. Forms and shoring. The construction of a cast-in-place structure involves three steps not encountered in the construction of steel or timber structures. These are ( a the construction of the forms, ( b the removal of these forms, and (c propping or shoring the

25、 new concrete to support its weight until its strength is adequate. Each of these steps involves labor and / or materials, which are not necessary with other forms of construction.3. Relatively low strength per unit of weight for volume. The compressive strength of concrete is roughly 5 to 10% that

26、of steel, while its unit density is roughly 30% that of steel. As a result, a concrete structure requires a larger volume and a greater weight of material than does a comparable steel structure. As a result, long-span structures are often built from steel.4. Time-dependent volume changes.Both concre

27、te and steel undergo-approximately the same amount of thermal expansion and contraction. Because there is less mass of steel to be heated or cooled, and because steel is a better concrete, a steel structure is generally affected by temperature changes to a greater extent than is a concrete structure

28、. On the other hand, concrete undergoes frying shrinkage, which, if restrained, may cause deflections or cracking. Furthermore, deflections will tend to increase with time, possibly doubling, due to creep of the concrete under sustained loads.In almost every branch of civil engineering and architect

29、ure extensive use is made of reinforced concrete for structures and foundations. Engineers and architects requires basic knowledge of reinforced concrete design throughout their professional careers. Much of this text is directly concerned with the behavior and proportioning of components that make

30、up typical reinforced concrete structures-beams,columns, and slabs. Once the behavior of these individual elements is understood, the designer will have the background to analyze and design a wide range of complex structures, such as foundations, buildings, and bridges, composed of these elements.Si

31、nce reinforced concrete is a no homogeneous material that creeps, shrinks, and cracks, its stresses cannot be accurately predicted by the traditional equations derived in a course in strength of materials for homogeneous elastic materials. Much ofreinforced concrete design in therefore empirical, i.

32、e., design equations and design methods are based on experimental and time-proved results instead of being derived exclusively from theoretical formulations.A thorough understanding of the behavior of reinforced concrete will allow the designer to convert an otherwise brittle material into tough duc

33、tile structural elements and thereby take advantage of concretes desirable characteristics, i ts high compressive strength, its fire resistance, and its durability.Concrete, a stone like material, is made by mixing cement, water, fine aggregate ( often sand , coarse aggregate, and frequently other a

34、dditives ( that modify properties into a workable mixture. In its unhardened or plastic state, concrete can be placed in forms to produce a large variety of structural elements. Although the hardened concrete by itself, i.e., without any reinforcement, is strong in compression, it lacks tensile stre

35、ngth and therefore cracks easily. Because unreinforced concrete is brittle, it cannot undergo large deformations under load and fails suddenly-without warning. The addition fo steel reinforcement to the concrete reduces the negative effects of its two principal inherent weaknesses, its susceptibilit

36、y to cracking and its brittleness. When the reinforcement is strongly bonded to the concrete, a strong, stiff, and ductile construction material is produced. This material, called reinforced concrete, is used extensively to construct foundations, structural frames, storage takes, shell roofs, highwa

37、ys, walls, dams, canals, and innumerable other structures and building products. Two other characteristics of concrete that are present even when concrete is reinforced are shrinkage and creep, but the negative effects of these properties can be mitigated by careful design.A code is a set technical

38、specifications and standards that control important details of design and construction. The purpose of codes it produce structures so that the public will be protected from poor of inadequate and construction.Two types f coeds exist. One type, called a structural code, is originated and controlled b

39、y specialists who are concerned with the proper use of a specific material or who are involved with the safe design of a particular class of structures.The second type of code, called a building code, is established to cover construction in a given region, often a city or a state. The objective of a

40、 building code is also to protect the public by accounting for the influence of the local environmental conditions on construction. For example, local authorities may specify additional provisions to account for such regional conditions as earthquake, heavy snow, or tornados. National structural cod

41、es genrally are incorporated into local building codes.The American Concrete Institute ( ACI Building Code covering the design of reinforced concrete buildings. It contains provisions covering all aspects of reinforced concrete manufacture, design, and construction. It includes specifications on qua

42、lity of materials, details on mixing and placing concrete, design assumptions for the analysis of continuous structures, and equations for proportioning members for designforces.All structures must be proportioned so they will not fail or deform excessively under any possible condition of service. T

43、herefore it is important that an engineer use great care in anticipating all the probable loads to which a structure will be subjected during its lifetime.Although the design of most members is controlled typically by dead and live load acting simultaneously, consideration must also be given to the

44、forces produced by wind, impact, shrinkage, temperature change, creep and support settlements, earthquake, and so forth.The load associated with the weight of the structure itself and its permanent components is called the dead load. The dead load of concrete members, which is substantial, should ne

45、ver be neglected in design computations. The exact magnitude of the dead load is not known accurately until members have been sized. Since some figure for the dead load must be used in computations to size the members, its magnitude must be estimated at first. After a structure has been analyzed, th

46、e members sized, and architectural details completed, the dead load can be computed more accurately. If the computed dead load is approximately equal to the initial estimate of its value ( or slightly less , the design is complete, but if a significant difference exists between the computed and esti

47、mated values of dead weight, the computations should be revised using an improved value of dead load. An accurate estimate of dead load is particularly important when spans are long, say over 75 ft ( 22.9 m , because dead load constitutes a major portion of the design load.Live loads associated with

48、 building use are specific items of equipment and occupants in a certain area of a building, building codes specify values of uniform live for which members are to be designed.After the structure has been sized for vertical load, it is checked for wind in combination with dead and live load as speci

49、fied in the code. Wind loads do not usually control the size of members in building less than 16 to 18 stories, but for tall buildings wind loads become significant and cause large forces to develop in the structures. Under these conditions economy can be achieved only by selecting a structural syst

50、em that is able to transfer horizontal loads into the ground efficiently.鋼筋混凝土 在每一個(gè)國(guó)家，混凝土及鋼筋混凝土都被用來(lái)作為建筑材料。很多地區(qū)，包 括美國(guó)和加拿大，鋼筋混凝土在工程建設(shè)中是主要的結(jié)構(gòu)材料。鋼筋混凝土建筑 的普遍性源于鋼筋的廣泛供應(yīng)和混凝土的組成成分，礫石，沙子，水泥等，混凝 土施工所需的技能相對(duì)簡(jiǎn)單，與其他形式的建設(shè)相比，鋼筋混凝土更加經(jīng)濟(jì)?；?凝土及鋼筋混凝土用于橋梁、各種地下結(jié)構(gòu)建筑、水池、電視塔、海洋石油勘探 建筑、工業(yè)建筑、大壩，甚至用于造船業(yè)。 鋼筋混凝土結(jié)構(gòu)可能是現(xiàn)澆混凝土結(jié)構(gòu)，在其最后位

51、置建造，或者他們可能 是在一家工廠生產(chǎn)混凝土預(yù)制件，再在施工現(xiàn)場(chǎng)安裝?；炷两Y(jié)構(gòu)在設(shè)計(jì)上可能 是普通的和多功能的，或形狀和布局是奇想和藝術(shù)的。其他很少幾種建材能夠提 供建筑和結(jié)構(gòu)如此的通用性和廣泛適用性。 混凝土有較強(qiáng)的抗壓力但抗拉力很弱。因此，混凝土，每當(dāng)承受荷載時(shí)，或 約束收縮或溫度變化，引起拉應(yīng)力，在超過(guò)抗拉強(qiáng)度時(shí)，裂縫開(kāi)始發(fā)展。在素混 凝土梁中，中和軸的彎矩是由在混凝土內(nèi)部拉壓力偶來(lái)抵抗作用荷載之后的值。 這種梁當(dāng)出現(xiàn)第一道裂縫時(shí)就突然完全地?cái)嗔蚜?。在鋼筋混凝土梁中，鋼筋是?樣埋置于混凝土中，以至于當(dāng)混凝土開(kāi)裂后彎矩平衡所需的拉力由綱筋中產(chǎn)生。 鋼筋混凝土構(gòu)件的建造包括以被建構(gòu)件的形

52、狀支摸板。模型必須足夠強(qiáng)大， 以至于能夠支承自重和濕混凝土的靜水壓力，工人施加的任何力量都適用于它， 具體的手推車(chē)， 風(fēng)壓力， 等等。 在混凝土的運(yùn)作過(guò)程中， 鋼筋將被放置在摸板中。 在混凝土硬化后，模板都將被移走。當(dāng)模板被移走時(shí)，支撐將被安裝來(lái)承受混凝 土的重量直到它達(dá)到足夠的強(qiáng)度來(lái)承受自重。 設(shè)計(jì)師必須使混凝土構(gòu)件有足夠的強(qiáng)度來(lái)抵抗荷、 載和足夠的剛度來(lái)防止過(guò) 度的撓度變形。除此之外，梁必須設(shè)計(jì)合理以便它能夠被建造。例如，鋼筋必須 按構(gòu)造設(shè)計(jì)，以便能在現(xiàn)場(chǎng)裝配。由于當(dāng)鋼筋放入摸板后才澆筑混凝土，因此混 凝土必須能夠流過(guò)鋼筋及摸板并完全充滿摸板的每個(gè)角落。 被建成的結(jié)構(gòu)材料的選擇是混凝土，還

53、是鋼材、砌體，或木材，取決于是否 有材料和一些價(jià)值決策。 結(jié)構(gòu)體系的選擇是由建筑師或工程師早在設(shè)計(jì)的基礎(chǔ)上 決定的，考慮到下列因素： 1.經(jīng)濟(jì)。常常首要考慮的是結(jié)構(gòu)的總造價(jià)。當(dāng)然，這是隨著材料的成本和安 裝構(gòu)件的必需勞動(dòng)力改變的。然而，總投資常常更受總工期的影響，因?yàn)槌邪?和業(yè)主必須借款或貸款以便完成建設(shè)， 在建筑物竣工前他們從此項(xiàng)投資中將得不 到任何回報(bào)。在一個(gè)典型的大型公寓或商業(yè)項(xiàng)目中，建筑成本的融資將是總費(fèi)用 的一個(gè)重要部分。因此，金融儲(chǔ)蓄，由于快速施工可能多于抵消增加材料成本。 基于這個(gè)原因，設(shè)計(jì)師可以采取任何措施規(guī)范設(shè)計(jì)來(lái)減輕削減的成本。 在許多情況下，長(zhǎng)期的經(jīng)濟(jì)結(jié)構(gòu)可能比第一成本

54、更重要。因此，維修和耐久 性是重要的考慮因素。 2 .用于建筑與結(jié)構(gòu)功能適宜的材料。鋼筋混凝土體系經(jīng)常讓設(shè)計(jì)師將建筑 與結(jié)構(gòu)的功能相結(jié)合。 混凝土被放置在塑性條件下借助于模板和表面加工來(lái)造出 想要的形狀和結(jié)構(gòu)，這是它具有的優(yōu)勢(shì)。在提供成品樓或天花板表面時(shí)，這使得 平板或其他形式的板作為受力構(gòu)件。同樣，鋼筋混凝土墻壁能提供有吸引力的建 筑表面，還有能力抵御重力、風(fēng)力，或地震荷載。最后，大小和形狀的選擇是由 設(shè)計(jì)師而不是由提供構(gòu)件的標(biāo)準(zhǔn)決定的。 3 .耐火性。建筑結(jié)構(gòu)必須經(jīng)受得住火災(zāi)的襲擊，并且當(dāng)人員疏散及大火撲 滅之時(shí)建筑物仍然保持不倒。 鋼筋混凝土建筑特殊的防火材料及其他構(gòu)造措施情 況下，自身

55、具有 1-3 個(gè)小時(shí)的耐火極限。鋼結(jié)構(gòu)或木結(jié)構(gòu)必須采取防火措施才能 達(dá)到類(lèi)似的耐火極限。 4 .低維護(hù)?；炷翗?gòu)件本身比結(jié)構(gòu)鋼或木材構(gòu)件需要更少的維修。如果致 密，尤其如此，加氣混凝土已經(jīng)被用于暴露于大氣中的表面，如果在設(shè)計(jì)中已經(jīng) 采取謹(jǐn)慎措施，以提供足夠的排水和遠(yuǎn)離的結(jié)構(gòu)。必須采取的特別預(yù)防措施是讓 混凝土接觸到鹽，如除冰化學(xué)品。 5 .材料的供應(yīng)。砂、碎石、水泥和混凝土攪拌設(shè)備是被非常廣泛使用的， 以及鋼筋比結(jié)構(gòu)鋼更容易運(yùn)到多數(shù)工地。 因此， 鋼筋混凝土在偏遠(yuǎn)地區(qū)經(jīng)常使用。 另一方面，有一些因素可能會(huì)導(dǎo)致選擇鋼筋混凝土以外的材料。這些措施包 括： 1 .低抗拉強(qiáng)度?；炷恋目估瓘?qiáng)度是遠(yuǎn)低于

56、其抗壓強(qiáng)度（約 1 / 10 ） ， 因此，混凝土易經(jīng)受裂縫。在結(jié)構(gòu)用途時(shí)，用鋼筋承受拉力，并限制裂縫寬度在 允許的范圍內(nèi)來(lái)克服。不過(guò)，在設(shè)計(jì)和施工中如果不采取措施，這些裂縫可能會(huì) 有礙觀瞻，或可允許水的浸入。發(fā)生這種情況時(shí)，水或化學(xué)物質(zhì)如道路除冰鹽可 能會(huì)導(dǎo)致混凝土的惡化或污染。這種情況下，需要特別設(shè)計(jì)的措施。在水支擋結(jié) 構(gòu)這種情況下，需要特別的措施和/或預(yù)應(yīng)力，以防止泄漏。 2 .支摸。建造一個(gè)現(xiàn)澆結(jié)構(gòu)包括三個(gè)步驟，在鋼或木結(jié)構(gòu)的施工中是遇不 到的。這些都是（a）支摸 （b）拆摸（ c ） 安裝支撐，直至其達(dá)到足夠的強(qiáng) 度以支承其重量。上述每個(gè)步驟，涉及勞動(dòng)力和/或材料，在其他結(jié)構(gòu)形式中， 這是沒(méi)有必要的。 3 . 每單位重量或量的相對(duì)低強(qiáng)度。該混凝土抗壓強(qiáng)度大約是鋼材抗壓強(qiáng)度 5 至 10 ， ，而其單位密度大約是鋼材密度的 30 。因此，一個(gè)混凝土結(jié)構(gòu)， 與鋼結(jié)構(gòu)相比，需要較大的體積和較大重量的材料。因此，大跨度結(jié)構(gòu)，往往建 成鋼結(jié)構(gòu)。 4 .時(shí)間依賴的量的變化。混凝土與鋼進(jìn)行大約同樣數(shù)量的熱膨脹和收縮時(shí)， 有比較少量的鋼材加熱或冷卻，因?yàn)殇撆c混凝土相比是一個(gè)較好的導(dǎo)體，鋼結(jié)構(gòu) 比混凝土結(jié)構(gòu)在更大程度上更易受溫度變化