土木工程畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯-鋼筋混凝土

1、 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)。混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

2、夠提供建筑和結(jié)構(gòu)如此的通用性和廣泛適用性?；炷劣休^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)嗔蚜恕Ｔ阡摻罨炷亮褐校摻钍悄菢勇裰糜诨炷林?，以至于?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，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

3、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

4、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毯蜆I(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

5、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

6、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。混凝土的抗拉強(qiáng)度是遠(yuǎn)低于其抗壓強(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。

7、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

8、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。另一方面，混凝土經(jīng)歷了干縮，如果被抑制，可能會(huì)導(dǎo)致變形或開(kāi)裂。此外，變形隨著時(shí)間的推移將趨于增加，由于混凝土在持續(xù)的負(fù)荷下的徐變，可能會(huì)增加一倍。幾乎在土木工程和建筑的每一個(gè)分支中，鋼筋混凝土在結(jié)構(gòu)和基礎(chǔ)領(lǐng)域內(nèi)都得到了廣泛的使用。因此，工程師及建筑師在其整個(gè)職業(yè)生涯中需要鋼筋混凝土設(shè)計(jì)的基本知識(shí)。文章的大部分是直接關(guān)于組成典型的鋼筋混凝土結(jié)構(gòu)的部件如梁、柱和板他們之間的作用、協(xié)調(diào)。一旦這些個(gè)別要素的作用被理解，設(shè)計(jì)師將有能力分析和設(shè)計(jì)這些元素組成的各種各樣的復(fù)雜結(jié)構(gòu)，例

9、如地基，建筑物和橋梁。由于鋼筋混凝土是一個(gè)徐變、收縮，并出現(xiàn)裂縫的非勻質(zhì)材料，它的應(yīng)力不能由適用于材料強(qiáng)度均勻彈性材料的傳統(tǒng)方程推導(dǎo)出的方程準(zhǔn)確預(yù)測(cè)。因此，許多鋼筋混凝土的設(shè)計(jì)基于實(shí)證，即設(shè)計(jì)方程和設(shè)計(jì)方法是基于實(shí)驗(yàn)和費(fèi)時(shí)的證明，而不是從理論的提法被完全導(dǎo)出的結(jié)果。對(duì)鋼筋混凝土性能徹底的了解將允許設(shè)計(jì)師將脆性材料轉(zhuǎn)換變成強(qiáng)硬的韌性結(jié)構(gòu)材料，從而利用混凝土良好的特點(diǎn)，其高抗壓強(qiáng)度，其耐火性，其耐久性。 混凝土-石狀的物質(zhì)，是由攪拌水泥，水，細(xì)骨料（通常砂），粗骨料，并經(jīng)常添加其他外加劑（即改善特性）而成為的一種和易性好的混合物。在其未硬化或塑性狀態(tài)下，混凝土可放置在模板里產(chǎn)生大量的各種結(jié)構(gòu)要素。

10、雖然硬化的混凝土本身，也就是說(shuō)，沒(méi)有任何鋼筋，它具有較強(qiáng)的抗壓強(qiáng)度，但缺乏抗拉強(qiáng)度，因此很容易產(chǎn)生裂縫。因?yàn)闊o(wú)鋼筋的混凝土是脆性的，它在荷載作用下不能進(jìn)行大變形，并在沒(méi)有預(yù)兆下突然斷裂。鋼筋與混凝土相結(jié)合，可以減少其主要的兩個(gè)固有弱點(diǎn)的負(fù)面影響，其易開(kāi)裂性和其脆性。當(dāng)鋼筋牢固黏結(jié)于混凝土?xí)r，一種強(qiáng)大、剛性、延性的建筑材料就誕生了。這種材料，所謂的鋼筋混凝土，被廣泛用于建筑基礎(chǔ)、結(jié)構(gòu)框架、倉(cāng)庫(kù)、網(wǎng)狀結(jié)構(gòu)、公路、墻壁、水壩、運(yùn)河及無(wú)數(shù)的其他結(jié)構(gòu)和建筑產(chǎn)品?；炷恋钠渌麅蓚€(gè)特點(diǎn)，是混凝土被加固時(shí)會(huì)發(fā)生收縮和徐變，但采用仔細(xì)的設(shè)計(jì)可以減輕這些特性的負(fù)面影響。 規(guī)范，是一套技術(shù)規(guī)格和控制設(shè)計(jì)與施工重要細(xì)

11、節(jié)的標(biāo)準(zhǔn)。規(guī)范的目的是產(chǎn)生合理的結(jié)構(gòu)，使使用者將免于劣質(zhì)和不合格的設(shè)計(jì)和結(jié)構(gòu)。現(xiàn)有兩種規(guī)范。其中一類，所謂的結(jié)構(gòu)規(guī)范，是源于關(guān)心正確使用具體材料或關(guān)心某一特定類別結(jié)構(gòu)安全設(shè)計(jì)的專家。第二種類型的規(guī)范，所謂的建筑條例，涵蓋了建設(shè)在某一地區(qū)，往往是一個(gè)城市或一個(gè)國(guó)家的建筑。建筑條例的目標(biāo)，也是以對(duì)抗當(dāng)?shù)丨h(huán)境條件對(duì)建設(shè)的影響來(lái)保障公眾的權(quán)益。例如，地方當(dāng)局可以規(guī)定其他的條款，以對(duì)抗這樣的區(qū)域條件，地震、大雪或龍卷風(fēng)。國(guó)家結(jié)構(gòu)規(guī)范常常被納入當(dāng)?shù)氐慕ㄖㄒ?guī)。美國(guó)混凝土學(xué)會(huì)（ ACI ）的建筑規(guī)范包括鋼筋混凝土建筑物的設(shè)計(jì)。它包括涵蓋鋼筋混凝土制造的各個(gè)方面-設(shè)計(jì)和施工的條文。它包括材料質(zhì)量的規(guī)格、混合和

12、現(xiàn)澆混凝土的細(xì)節(jié)，連續(xù)結(jié)構(gòu)分析的設(shè)計(jì)假定，配料成分的設(shè)計(jì)方程。所有構(gòu)件必須協(xié)調(diào)，這樣它們?cè)谌魏慰赡艿墓ぷ鳁l件下就不會(huì)失效或發(fā)生過(guò)大變形。因此，一名工程師非常謹(jǐn)慎地預(yù)期結(jié)構(gòu)在其一生中所有可能經(jīng)受的荷載，這是非常重要的。雖然大部分構(gòu)件的設(shè)計(jì)是由同時(shí)作用的恒載和活載所控制，但還必須考慮到風(fēng)、沖擊、收縮、溫度變化、徐變和地基沉陷、地震等等所產(chǎn)生的的力。 與結(jié)構(gòu)自重和固有的構(gòu)件重量有關(guān)的荷載稱為恒載。混凝土構(gòu)件的恒載是固有的，在設(shè)計(jì)計(jì)算過(guò)程中是必須要考慮的。恒載值的大小直到構(gòu)件尺寸確定后才能清楚的知道 。由于恒載的一些數(shù)值在計(jì)算構(gòu)件尺寸時(shí)要用到，所以首先要估計(jì)他們值的大小。在結(jié)構(gòu)進(jìn)行了分析構(gòu)件、構(gòu)件尺寸

13、確定、建筑的細(xì)節(jié)完成后，恒載可以計(jì)算更準(zhǔn)確。如果計(jì)算的恒載大約等于它的初步估計(jì)值（或略少） ，但設(shè)計(jì)完成后，如果計(jì)算值和估計(jì)值之間存在顯著性差異時(shí)，計(jì)算應(yīng)用改進(jìn)的恒載值加以修正。當(dāng)跨度較長(zhǎng)時(shí)，恒載的準(zhǔn)確估計(jì)是特別重要的，因?yàn)楫?dāng)跨度超過(guò)七十五英尺（ 22.9米）時(shí) ，恒載是設(shè)計(jì)荷載的一個(gè)重要組成部分。建設(shè)使用的相關(guān)活荷載是由城市或國(guó)家結(jié)構(gòu)規(guī)范規(guī)定的。設(shè)計(jì)構(gòu)件均布活荷載的值是由結(jié)構(gòu)規(guī)范規(guī)定的，而不是根據(jù)設(shè)備的特定項(xiàng)目和某一個(gè)特定地區(qū)的使用者來(lái)估計(jì)。 結(jié)構(gòu)在豎向荷載下定了尺寸后，還要根據(jù)風(fēng)荷載和規(guī)范中規(guī)定的恒載活載組合后的結(jié)果來(lái)進(jìn)行驗(yàn)算。風(fēng)荷載在少于16到18層樓房中通常不控制構(gòu)件的大小，但對(duì)于高層

14、建筑，風(fēng)荷載在結(jié)構(gòu)中成為重要的控制因素和引起強(qiáng)大作用力的因素。在這種情況下，只有選擇一個(gè)能夠有效地將橫向荷載傳遞到地面的結(jié)構(gòu)體系，經(jīng)濟(jì)才能實(shí)現(xiàn)。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 constructi

15、on. The universal nature of reinforced concrete construction stems from 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

16、 of construction. Concrete and reinforced concrete are used in bridges, 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

17、 in their final location, or they may be precast concrete produced in a 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 ve

18、rsatility and scope.Concrete is strong in compression but weak in tension. 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 neut

19、ral axis due to applied loads are resisted by an internal tension-compression 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 for

20、ces needed for moment equilibrium after the concrete cracks can be developed 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

21、 wet concrete, and any forces applied to it by workers, concrete buggies, 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 su

22、pport the weight of the concrete until it has reached sufficient strength 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 co

23、nstructed. For example, the reinforcement must be detailed so that it can 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 completel

24、y.The choice of whether a structure should be built of concrete, steel, 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. E

25、conomy. Frequently, the foremost consideration is the overall const of the 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 contr

26、actor and owner must borrow or otherwise allocate money to carry out the 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 t

27、he total cost. As a result, financial savings due to rapid construction may 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

28、structure may be more important than the first cost. As a result, maintenance 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 funct

29、ions. Concrete has the advantage that it is placed in a plastic condition 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 flo

30、or and / or ceiling surfaces. Similarly, reinforced concrete walls can provide 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 man

31、ufactured members.3. Fire resistance. The structure in a building must withstand 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. Struct

32、ural steel or timber buildings must be fireproofed to attain similar fire 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

33、atmosphere, and if care has been taken in the design to provide adequate drainage 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 wid

34、ely available, and reinforcing steel can be transported to most job sites 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 a material other than reinforced concrete

35、. These include:1. Low tensile strength. The tensile strength concrete is much 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

36、 values. Unless care is taken in design and construction, however, these cracks 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.

37、In the case of water-retaining structures, special details and / of prestressing 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 constructio

38、n of the forms, ( b ) the removal of these forms, and (c) propping or shoring the 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

39、weight for volume. The compressive strength of concrete is roughly 5 to 10% that 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 s

40、tructures are often built from steel.4. Time-dependent volume changes. Both concrete 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 generall

41、y affected by temperature changes to a greater extent than is a concrete structure. 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 concre

42、te under sustained loads.In almost every branch of civil engineering and architecture 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

43、is directly concerned with the behavior and proportioning of components that make 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 str

44、uctures, such as foundations, buildings, and bridges, composed of these elements.Since 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 homogene

45、ous elastic materials. Much of reinforced concrete design in therefore empirical, i.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 conc

46、rete will allow the designer to convert an otherwise brittle material into tough ductile structural elements and thereby take advantage of concretes desirable characteristics, its high compressive strength, its fire resistance, and its durability.Concrete, a stone like material, is made by mixing ce

47、ment, water, fine aggregate ( often sand ), coarse aggregate, and frequently other additives ( 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 it

48、self, i.e., without any reinforcement, is strong in compression, it lacks tensile strength 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 re

49、duces the negative effects of its two principal inherent weaknesses, its susceptibility 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 exten

50、sively to construct foundations, structural frames, storage takes, shell roofs, highways, 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 eff

51、ects of these properties can be mitigated by careful design.A code is a set technical 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 t

52、ypes f coeds exist. One type, called a structural code, is originated and controlled by 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 establishe

53、d to cover construction in a given region, often a city or a state. The objective of a 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 su

54、ch regional conditions as earthquake, heavy snow, or tornados. National structural codes 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 rein

55、forced concrete manufacture, design, and construction. It includes specifications on quality of materials, details on mixing and placing concrete, design assumptions for the analysis of continuous structures, and equations for proportioning members for design forces.All structures must be proportion

56、ed so they will not fail or deform excessively under any possible condition of service. Therefore 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 th