++m連續(xù)剛構(gòu)橋設(shè)計(jì)

頁致謝殖通過緒為期敢兩個(gè)面月的笨畢業(yè)吩設(shè)計(jì)坦，讓織我深逢深的案體會(huì)耗到合腸作的芽作用息遠(yuǎn)遠(yuǎn)膜大于陜一個(gè)暢人的住作用世，所刊以感僅謝全慨組的睬同學(xué)話給我胡提供胳的幫螞助，閘以及蒸指導(dǎo)喘老師孔的悉食心輔香導(dǎo)。牢可以驚說，盲沒有斗指導(dǎo)祖老師芬的關(guān)粗心、滔指導(dǎo)差與鼓長勵(lì)，移就不蔬可能拍有本琴設(shè)計(jì)替的誕止生，噸在此瞞我向償他致膠意最甜崇高逆的敬覺意和伐表示稍衷心久的感熊謝！燥同時(shí)拋，要踏感謝屑學(xué)院欣給予蝕我這破樣一臂次機(jī)肥會(huì)，箭能夠屑獨(dú)立紙地完澡成一襲個(gè)設(shè)葬計(jì)，捎并在彼這個(gè)互過程克當(dāng)中耐，給捆予我覽們各倡種方集便，啞使我玻能夠井更多叼學(xué)習(xí)閑一些劃實(shí)踐詠應(yīng)用腳知識(shí)攤，增違強(qiáng)了挎我們驗(yàn)實(shí)踐甩操作誕和動(dòng)深手應(yīng)衣用能惠力，槍提高更了獨(dú)海立思示考的姐能力偉。畢酒業(yè)設(shè)跑計(jì)的程完成捧將為姿以后津的工碗作打網(wǎng)好堅(jiān)線實(shí)的煤基礎(chǔ)鳳。再白次對(duì)地各位夢(mèng)老師欣和同撥學(xué)表息示我笑最誠章?lián)吹纳w感謝成，謝些謝你挽們！抗參考兩文獻(xiàn)企[1廟]嫩抖《公打路鋼芝筋混覽凝土翁及預(yù)宇應(yīng)力膝混凝展土橋溉涵設(shè)品計(jì)規(guī)婦范》遍（潔JT碑G而D6弟2皺—貧20網(wǎng)04寬圾）蠢[2傘]賓完《公芝路橋系涵設(shè)悼計(jì)通耽用規(guī)咱范飄》駛循瓦炎仔杰社仆級(jí)哨撕裕（鍋JT風(fēng)G遼D6宰0糟—慕20蘆04叮姓）艇[3洽]甜血《城濤市橋曬梁設(shè)趴計(jì)規(guī)竟范哲》碧焦醒殖各索戴羅彩攀陵歲獵碌（路CJ拋J計(jì)11眉-2踢01壁1皂決）前[4睬]忘渠《橋兄梁工坑程》杰中國斑建筑謝工業(yè)座出版肥社矛[5覺]牢脹《橋摸梁施鋼工》療中國冶鐵道儀出版向社南[6咬]渠完《中主華人食民共艱和國侵行業(yè)綿推薦扎性標(biāo)稼準(zhǔn)歲(J水TG騎/T纏H茄21仿-2憶01沫1)飄:雖公路呀橋梁著技術(shù)免狀況產(chǎn)評(píng)定陣標(biāo)準(zhǔn)睡》案[7垮]獎(jiǎng)睜《橋蹲梁工錄程》葛人民景交通出出版陣社輩[8馳]前遙《結(jié)印構(gòu)力販學(xué)控》手.2煉00巖7腹年槍1吳2疤月問第焰3嶺版堡.跟武漢悲理工唉大學(xué)器出版煩社秒.瞞[9辣]遲誓《橋籮梁設(shè)間計(jì)與胸計(jì)算病》煌.2廈00貨7戰(zhàn)年鈔2致月圍第纖1枕版粒.凍人民鉗交通竄出版閑社障附錄攪解工程寶圖紙擱（廁1豈）設(shè)也計(jì)說踢明肚（橫2者）橋并梁總擋體布膝置圖粉（迎3膨）梁香段施躬工順覺序圖鹿（月4邁）箱斷梁構(gòu)霜造圖居（一騙）撲（抬5攤）箱福梁構(gòu)透造圖僵（二筐）崗（令6江）箱爸梁構(gòu)嫂造圖獻(xiàn)（三盛）固（據(jù)7熱）箱啊梁鋼遮束圖?。ㄒ焕妫┲u8害）箱拆梁鋼話束圖阿（二添）灑（學(xué)9潮）箱傅梁鋼則束圖參（三咳）蹦2招.津外文叔文獻(xiàn)鵝翻譯載混凝辭土悠混凝鳳土是舅一種再類似與石頭索的材勇料，凝它是蓬把水燙加入塔強(qiáng)度村水泥弱、砂皇和骨捐料的冠混合歸物中郵而形賢成的粗。在薪水泥機(jī)中水暴引起舌了化回學(xué)反研應(yīng)，毛結(jié)果鉆，水帳泥漿之和水的牢固艷的結(jié)廚合在聚一起蟻，并潔把砂紗子和煉骨料示牢固殖的嵌賭入里株面，狀就形夜成了年堅(jiān)固譽(yù)、密停實(shí)的球物質(zhì)扮。混素凝土梳是一細(xì)種有赤很高劣抗壓王強(qiáng)度收低抗框拉強(qiáng)導(dǎo)度的悅材料世?；斓哪猎伒目菇y(tǒng)拉強(qiáng)列度非文常的酸低，灰大約變?yōu)榭巩a(chǎn)壓強(qiáng)悲度的司十分斯之一球。思水泥憐是一蓄種有僵著黏桿結(jié)力劑和固論結(jié)力輔特性念的材賴料，泥它能灘夠把谷各種鄉(xiāng)礦物相顆粒帶很好風(fēng)的結(jié)條合到舌一起偷。用景于建姻筑的旱水泥衡具有踩在水斑中凝巷結(jié)和牌硬化春的性玉能，租通常因稱作城水硬籍水泥宿，又體細(xì)分唐為天犧然水紐泥、掩波特憶蘭水酒泥和昆礬土寫水泥魯混凝欲土作毛為建息筑材饑料已逗經(jīng)好爹幾個(gè)絞世紀(jì)宜了。箏在十倘九世蹄紀(jì)早繼期，毛人造液波蘭積特水剝泥就炒被發(fā)許明了輸，現(xiàn)搞在這隔種材桐料還霸廣泛談的用短于建蟲造房或屋的鄰混凝即土中架?；煺夏翐鹾弯摽〗钍怯炎钇諙|通的蠻建筑糾材料攀。它洗們有六時(shí)互艙相補(bǔ)康充，驗(yàn)有時(shí)梁相互商作用濃，因獵此這麻些材喂料可字用于繞建造長形式迷相似杯和功鼓能的喝建筑感物。粗而且令，工托程師堵一般忙知道則的結(jié)科構(gòu)混制凝土崇比鋼攻筋要提少。朝在混盲凝土孔結(jié)構(gòu)棕中是扎不同夫的。勤確黎實(shí)兇,躍水泥勇的質(zhì)鏟量如野同鋼錦材一粘樣溝,背也是腔由生翼產(chǎn)廠其家來扯保證擠的夏,棗只要闖選擇提適當(dāng)傻的水用泥滲,扒它就夠決不橋會(huì)成飽為混澆凝土腰結(jié)構(gòu)大不合在格的央原因焰。繪令人盟驚奇濃的贊是百,袖優(yōu)質(zhì)農(nóng)混凝閑土配劑料的渠各組感分與麗劣質(zhì)廈混凝王土的王完全不相堵同然,千而正皂是這屬種筍“山專門濕技廟術(shù)腔”冰（然勉而往噸往無拴需增暑加工煉作量停）決督定著嫌兩種蔬混凝故土的腎差別甲。蜂近年痰來對(duì)引混凝去土的芬各種脖性能桑如密揉實(shí)度浙，耐剛久性釋，抗笛拉強(qiáng)波度，聚抗?jié)B浴透性曠，耐姑磨性憶，抗百硫酸識(shí)鹽浸誕蝕以蘿及其獨(dú)他一攏些性躺能的兇興趣丹大為宰增長哪，因由為現(xiàn)毀代規(guī)膊范需限要闡弱明對(duì)我混凝援土特而殊性址能的眾要求衛(wèi)，而宇不是研簡(jiǎn)單灰地規(guī)霧范混陰凝土縱組成鄰材料摧的數(shù)尚量和習(xí)質(zhì)量房。茅1.娛慧混凝司土的阿強(qiáng)度但混凝韻土的儲(chǔ)強(qiáng)度抵通常霜被認(rèn)累為它細(xì)具有康價(jià)值讓的性崖能實(shí)傭際上臥是很幼重要微的，惑在許發(fā)多實(shí)鋸際的腿工程仍中另墊一些典特性錯(cuò)，例轟如耐護(hù)久性蒸和抗萌滲透洽性。但骨料籌一般軍被認(rèn)挎為是肯一種惑惰性右材料島，由窗于經(jīng)們濟(jì)原積因認(rèn)野為它思和水媽泥不邀能很卻好的蜜黏結(jié)向。但刺從相厲反的泛觀點(diǎn)丟來看劉，也菊可把廊骨料夢(mèng)看成野是一僚種建留筑材斷料，倍借助茶于水炕泥漿恒，就睜像圬猴工建濱筑一慢樣，惰連接刻成一幣個(gè)粘津聚性期整體兆。棄事實(shí)奴上，謠骨料棉不是湊真正馳的惰敞性材蜜料，刮它的宇物理六特性躺溫度唯，化乎學(xué)特徑性影宇響著污混凝圣土的筐質(zhì)量借。魔骨料弱比水引泥便額宜，吩因此倦，在糠混凝栗土拌欣合料嶼中盡歸量多鑄用骨捆料而鳳少用拐水泥榨是經(jīng)棚濟(jì)的餃。救2.孔俊混凝絮土的預(yù)養(yǎng)護(hù)雄在早帥期硬生化階標(biāo)段，逮混凝午土在餃適宜赴的環(huán)繡境中夠養(yǎng)護(hù)半，適云當(dāng)?shù)耐痘旌橡嚨玫綄?yōu)質(zhì)披的混取凝土老。養(yǎng)旬護(hù)是消用于愈提高屬水泥弦水化泛的一擱種措韻施，良它通泉過控啟制溫廁度和磁濕度鼓使混典凝土源完全剃硬化愉。編更確甩切的詳說，祝養(yǎng)護(hù)種的目炎的是精要使里混凝養(yǎng)土保躺持或護(hù)盡可掛能接商近于憶飽和歐狀態(tài)如，直抹至新軌鮮水秀泥漿瞧中原摸始充袖水空講間為慘水泥茅水化理物填參充到答所要稈求的猜程度所為止娘。在?；炷h土痛中餓,排在水貴化達(dá)領(lǐng)到接梯近最生大值只時(shí)養(yǎng)鏈護(hù)作優(yōu)用開蔬始發(fā)址生肉.新養(yǎng)護(hù)段的必瘋要性傲事實(shí)印上是若水泥廚的水汗化作木用只蜂發(fā)生揚(yáng)在充約水的房毛細(xì)茫管中格。由佳于這擱個(gè)原泛因，響必須延阻止哥一些垮水從主毛細(xì)杠管中劃蒸發(fā)遵，而防且水罩蒸發(fā)眨形成呼的自伴干作袋用必領(lǐng)然被佩外界岸的水怎所代直替。哭因此漆，自集干作叮用在視水灰勞比低遲于勸0.執(zhí)5竹左右耍的拌邀和物咐中才副有其微重要世性；鑄至于鞠在高辱水灰怠比的率情況沒下，備密封閘試件應(yīng)的水予化速斤度則奴與飽街和試錄件的駕水化太速度寫相同歸。這約一說于明十捕分重魯要，襖因?yàn)榉逶瘸缭J(rèn)抵為只睡要混碌凝土斥拌和沃物水枝量超念過與套水泥音水化蝴反應(yīng)靜所需群用水箱量，占則在銹硬化漂期間脹即使殿有少德量的灣失水廣也不貧會(huì)對(duì)瓣硬化元過程柔和強(qiáng)佛度的夢(mèng)增長田產(chǎn)生嘩有害夏的影綢響。螞3虛.洲混凝雖土的遣徐變攜與收魔縮拔如同雙許多鵲其他走的建同筑材貴料混恢凝土理存在擱著一慰定程另度的暢彈性注，然垂而，妥在持很續(xù)的圈荷載雀作用粗下，掏隨著南時(shí)間桂的增陰長應(yīng)剖變也策增長稀。例蛋如：靈混凝卵土出絡(luò)現(xiàn)徐機(jī)變現(xiàn)悠象，食另外出，無俗論構(gòu)馬件是繞否承尸受荷丟載，橋混凝株土因昨干燥萄縮小巾產(chǎn)生條收縮事。驚混凝憶土的忌應(yīng)變繭與應(yīng)謝力的漠關(guān)系王是一記個(gè)時(shí)短間函腦數(shù)，前一般誰隨著凳時(shí)間辰應(yīng)變巡的增表長是彩由于應(yīng)混凝樂土徐然變。南混凝羨土構(gòu)斷件的刷徐變牙量與靈應(yīng)力廟的大贊小要,配應(yīng)力脂作用近時(shí)間達(dá)的長椒短黨,讀施加序應(yīng)力頸時(shí)混轎凝土雁的齡優(yōu)期與逢強(qiáng)度歲等都虛有關(guān)厭系。娃在鋼探筋混雷凝土注柱中策，徐部變一須般會(huì)目導(dǎo)致然荷載辯從混接凝土額傳到兼鋼筋寺混凝精土構(gòu)地件上嚷。一慶旦鋼拐筋發(fā)黎生屈蛇服，您荷載敢的任辟何增星加都受要混綱凝土狗承受謠，因屑此。隙在破魄壞之才前鋼宰筋與貴混凝敵土二首者的頑強(qiáng)度益都得趣到充擴(kuò)分利州用縱—賭—誓這一梢性質(zhì)皺已為效設(shè)計(jì)悄公式請(qǐng)所采價(jià)用。郊眾所暫周知冤，由妙于混胞凝土起的徐誕變產(chǎn)護(hù)生的撞預(yù)應(yīng)舟力的甘損失手。確巧實(shí)，載它是袍造成舅所有斑構(gòu)件疏預(yù)應(yīng)碰力損呈失的瓦原因弓。只昌有采通用了單高強(qiáng)振度鋼點(diǎn)筋，般其延仿伸率胃數(shù)倍唇于混分凝土上徐變拋與收吩縮引苦起的余縮短奧，預(yù)卸應(yīng)力鉗技術(shù)溪才獲旋得成緒功。刮結(jié)構(gòu)敬中混掙凝土稀的收鬧縮的龍重要程性在暴于很鏟大程致度上第會(huì)導(dǎo)芒致裂沈縫。吹然而礙，在尊普通頸的混亮合中羽通過額減少心用水捎量，劫材料報(bào)收縮煩可能語會(huì)減價(jià)少乘到瘦40繪%間。減倚少用素水量口是通冊(cè)過采予用高滿性能巡的塑賽化劑煉以進(jìn)屈一步膨降低遵用水先量，堵并采案取在徑較低斗的溫競(jìng)度下蓋養(yǎng)護(hù)悅混凝瞇土，淘使混陣凝土夕硬化殘時(shí)周寒圍的奔空氣女所吸棗收的哭水分束較少遮來實(shí)描現(xiàn)的悼。外4肅.芝鋼筋膠混凝與土光鋼筋生混凝蛙土因雕其強(qiáng)嫂度大探，經(jīng)滔久耐持用，袋可獲疏量大盡，適功應(yīng)性掙強(qiáng)而屆成為招一種故很適弊合許府多永鼻久型南建筑之物的渡經(jīng)濟(jì)解的建屯筑材銷料。習(xí)混凝疼土的幸抗拉近強(qiáng)度卸相對(duì)鳴的教仍高，棍能夠披有足崗夠的孕物質(zhì)雷去提訪供穩(wěn)咽定性通。另莊一方菜面，鏈鋼筋杠抗拉蠻強(qiáng)，吩但是廊由于花它的許柔弱汽的特施性會(huì)桐缺少欣足夠購的抗邀壓穩(wěn)深定性明。鋼日筋混規(guī)凝土誰構(gòu)件低中的奴混凝蕩土抵明抗壓渴力，藝鋼筋賓抵抗印拉力龍，因枕而是勾一個(gè)觀理想拼的結(jié)蔥構(gòu)關(guān)憤系。倚與當(dāng)卵前可眼行的叛其他耐建筑雁材料鍵相比償，建笨筑結(jié)速構(gòu)工酬程中開混凝瓦土的志廣泛杯應(yīng)用獲來源煙于它科的經(jīng)時(shí)濟(jì)性似。它鞏缺少池的抗樣拉強(qiáng)端度是騎通過孩鋼筋哭來克收服的波，通詠常，隔在鋼吊筋形款式中堵，生槐產(chǎn)一鄭種復(fù)是合材行料稱畫為鋼擋筋混縮凝土洪。冶雖然淋鋼筋益不能效防止巧混凝腥土受獎(jiǎng)拉區(qū)強(qiáng)裂縫婦的產(chǎn)敬生，泊但確焰實(shí)能勾限制狐裂縫俊的發(fā)熔展，隨因此屬提供例了抵摩抗內(nèi)法拉力糊的有半效手怨段。矮比起洋混凝啞土的跡用量樂，鋼牽筋的看數(shù)量進(jìn)通常推需要丘的少島，因書此鋼特筋混捕凝土驢建筑克物的豆總造嘆價(jià)在篩商業(yè)武上保菊持著瓶競(jìng)爭(zhēng)體性。踐因而住在由著于剪傷切和希彎曲騙聯(lián)合凳作用爛而使捧梁產(chǎn)拖生斜同裂縫掠的區(qū)忠域要礙放置膨成矩進(jìn)形配筒置的億垂直倘鋼筋栗和水匯平鋼縱筋。帝混凝稻土的逆開裂帖可能譜是由栗外界堂的荷渠載引夏起的漢，也宗可能花由溫皆度梯報(bào)度引壇起的斧。因繩此，銜輔助鋒鋼筋報(bào)能夠陡控制各這種撿可能掉細(xì)微港甚至彈危險(xiǎn)穩(wěn)的裂符縫。俯5喇.紐預(yù)應(yīng)嗚力混圍凝土艙混凝籌土是伙一種咸基本燥的抗惹壓的傳材料復(fù)。它姐的抗房拉強(qiáng)保度比采抗壓件強(qiáng)度個(gè)要低肉，在女許多籃的設(shè)晚計(jì)中分忽略拌它的版抗拉柏強(qiáng)度增。這價(jià)里所匪說的撫預(yù)應(yīng)槐力混賭凝土資一般克包括黑抗壓亮力的嶄應(yīng)用撈，預(yù)始先的逼在混嘗凝土判中施風(fēng)加設(shè)圓計(jì)的駱載荷脾，以雹致于貞抗拉穩(wěn)強(qiáng)度重的減嘴少或妙消失酒。因透此，舌對(duì)混臨凝土答預(yù)加板應(yīng)力門，本為質(zhì)上劇就是漿在施漁加預(yù)什期的爸設(shè)計(jì)悠荷載坦之前譯施加壘應(yīng)力弦載荷遣，以而使不青然會(huì)黑出現(xiàn)留的拉西應(yīng)力沖得以禁減少宰或被脹消除貿(mào)。反從改衛(wèi)善使塊用性廊能的標(biāo)意義底上來盞說，陳這樣斤的部文分預(yù)化加應(yīng)慚力，雪不僅鼻比普渣通鋼玉筋混籍凝土寫結(jié)構(gòu)投，而另且比益原來曲的全喘預(yù)應(yīng)脹力方叉式，擇都顯泊示出誕其重槳大改故進(jìn)，忍全預(yù)礦應(yīng)力壘方式豆雖然巷消除波了使諷用載琴荷下管的裂綢縫，趙但往嫂往產(chǎn)嘴生令鍬人傷扇腦筋診的上般拱度墊。沉先張醋法是捉一種碗非常領(lǐng)經(jīng)濟(jì)市的施棚加預(yù)仿應(yīng)力灶的方睬法，及不僅肆是由苦于設(shè)泥計(jì)的告標(biāo)準(zhǔn)改化可短以重洽復(fù)利施用鋼恥?；驒?quán)玻璃堪纖維御板，竊而且國也是媽因?yàn)橥瑫r(shí)老對(duì)許況多構(gòu)況件迅診速的午施加馳預(yù)應(yīng)嗚力，累結(jié)果丟大大兼節(jié)省搶勞力需。槍雖然孕錨固翻裝置承在本支身位尚置就需將預(yù)靈張拉源力傳歐給混瀉凝土肺。然帝而壓封漿可令改善潛構(gòu)件衰在超搏載時(shí)技的工半作性壩能，膀并增綢加構(gòu)嘗件的炊極限腰抗彎愛強(qiáng)度筐。燕Co鑰nc映re腳te譯Co恐nc稀re最te惠i纏s齡a菌ro嘴ck紫-l極ik弓e等ma式te霞ri范al曬p島ro牲du條ce定d訪by潑a屈dd華in巾g酒wa葬t(yī)e增r茫to傅a預(yù)m象ix工tu傾re詞o存f廟po取wd既er勾ed闖c反em蕩en澡t,或s士an初d暮,臂an熱d念st臂on腫es區(qū).模Wa暗te撕r軍ca圣us柏es蠅c歇he習(xí)mi曠ca抄l果re筒ac憐ti滾on抵s壯to悔t咱ak寬e拾pl永ac汽e稈in尚t執(zhí)he永c雪em禽en嘗t,雙a腿nd史a牌s互a奸re棟su埋lt繁,比th銅e愛pa丟st粘e齒of菠c掃em淺en笑t策an倉d擠wa鍵te覽r屬se增ts平h卷ar綠d頭an拜d高gr鬼ip旬s藏fi素rm月ly演t街he度s達(dá)an塊d穴an販d臣st懷on丑es詠e煮mb糾ed芹de眠d板in垃i閱t,乏f柏or壓mi逮ng攝a第s烈tr喇on叢g,劑d裕en榨se拒m市as執(zhí)s.剩C些on與cr飄et夾e萍is秋a事m蚊at晃er喝ia悲l爆wh繞ic陰h舅is蝦h話ig肺h嘆in基c藍(lán)om宋pr魯es覽si迎ve榨s曬tr啦en湊gt腰h幕bu網(wǎng)t趁lo桑w孤in骨t答en渠si車le而s吊tr臂en分gt桑h.池T雷he甜t菠en汁si哲le銹s左tr釘en遙gt鋼h葬of牲c(diǎn)趁on鍵cr盤et頌e鉤is套e烤xt虹re雕me概ly條l騰ow燥,六ab芽ou柏t臥on恭e-妻te去nt表h辰of休i離ts芹c盡om抱pr恒es槍si西ve貍s橫tr抹en胃gt碌h.Cementisamaterialwithadhesiveandcohesivepropertieswhichenableittobondmineralfragments.Thecementsusedinbuildinghavethepropertyofsettingandhardeningunderwaterandareusuallydescribedashydrauliccements,withsub-classificationsnatural,Portlandandaluminous.Concretehasbeenusedasabuildingmaterialforcenturies.IntheearlynineteenthcenturyartificialPortlandcementwasinvented,andthisisnowthematerialmostcommonlyusedinmakingconcreteforbuildings.Concreteandsteelarethemostcommonlyusedstructuralmaterials.Theysometimescomplementoneanother,andsometimescompetewithoneanothersothatstructuresofasimilartypeandfunctioncanbebuiltwitheitherofthesematerials.Andyet,theengineeroftenknowslessabouttheconcreteofwhichthestructureismadethanaboutthesteel.Onaconcretebuildingsitethesituationistotallydifferent.Itistruethatthequalityofcementisguaranteedbythemanufacturerinamannersimilartosteelandprovidedsuitablecementischosenitishardlyeveracauseoffaultsinaconcretestructure.Surprisingly,theingredientsofagoodconcreteareexactlythesame,anditisonlythe“know-how”,oftenwithoutadditionalcostoflabor,thatisresponsibleforthedifference.Interestinthevariouspropertiesofconcrete-density,durability,tensilestrength,impermeability,resistancetoabrasion,resistancetosulphateattack,andmanyothers-hasrecentlybeenheightenedsincemodernspecificationstendtostaterequirementsforparticularpropertiesofconcreteratherthansimplytostipulatethequalityandquantityoftheconstituentmaterials.1.StrengthofconcreteStrengthofconcreteiscommonlyconsidereditsmostvaluableproperty,althoughinmanypracticalcasesothercharacteristicssuchasdurabilityandimpermeabilitymayinfactbemoreimportant.Aggregatewasoriginallyviewedasaninertmaterialdispersedthroughoutthecementpastelargelyforeconomicreasons.Itispossible,however,totakeanoppositeviewandtolookonaggregateasabuildingmaterialconnectedintoacohesivewholebymeansofthecementpaste,inamannersimilartomasonryconstruction.Infact,aggregateisnottrulyinertanditsphysical,thermal,andsometimesalsochemicalpropertiesinfluencetheperformanceofconcrete.Aggregateischeaperthancementanditis,therefore,economicaltoputintothemixasmuchoftheformerandaslitterofthelatteraspossible.2.CuringofConcreteInordertoobtaingoodconcretetheplacingofanappropriatemixmustbefollowedbycuringinasuitableenvironmentduringtheearlystagesofhardening.Curingisthenamegiventoproceduresusedforpromotingthehydrationofcement.Itconsistsofcontrollingtemperatureandmoisturemovementintoandoutoftheconcrete. Morespecifically,theobjectofcuringistokeepconcretesaturated,orasnearlysaturatedaspossibleuntiltheoriginallywater-filledspaceinthefreshcementpastehasbeenfilledtothedesiredextentbytheproductsofthehydrationofthecement.Inthecaseofsiteconcrete,activecuringnearlyalwayslongbeforethemaximumpossiblehydrationhastakeplace.Thenecessityforcuringarisesfromthefactthatthehydrationofcementcantakeplaceonlyinwater-filledcapillariesmustbeprevented.Furthermore,waterlostinternallybyself-desiccationhastobereplacebywaterfromtheoutside,Self-desiccationisthusofimportanceinmixeswithwater/cementratiosbelowabout0.5,forhigherwater/cementratiostherateofhydrationofasealedspecimenequalsthatofasaturatedspecimen.Thisstatementisofconsiderableimportanceasitwasformerlythoughtthat,providedaconcretemixcontainedwaterinexcessofthatrequiredforthechemicalreactionswithcement,asmalllossofwaterduringhardeningwouldnotadverselyaffecttheprocessofhardeningandgainofstrength.3.CreepandShrinkageofConcreteLikemanyotherstructuralmaterials,concreteistoacertaindegreeelastic.Undersustainedloading,however,strainincreaseswithtime,i.e.concreteexhibitscreep.Inaddition,whethersubjectedtoloadornot,concretecontractsondrying,undergoingshrinkage.Therelationbetweenstressandstrainforconcreteisafunctionoftime:thegradualincreaseinstrainwithtimeisduetocreep.Creepinconcretemembersisdependentonthemagnitudeofthestress,thelengthoftimethatthestresshasbeenapplied,andtheageandstrengthoftheconcretewhenthestressisapplied.Inreinforcedconcretecolumns,creepresultsinagradualtransferofloadfromtheconcretetothereinforcement.Oncethesteelyields,anyincreaseinloadistakenbytheconcrete,sothatthefullstrengthofboththesteelandtheconcreteisdevelopedbeforefailuretakesplace—afactrecognizedbythedesignformulae.Thelossofpre-stressduetocreepiswellknownand,indeed,accountsforthefailureofallearlyattemptsatprestressing.Itwasonlytheintroductionofhightensilesteel,whoseelongationisseveraltimesthecontractionofconcreteduetocreepandshrinkagethatmadeprestrssingasuccessfulproposition.Theimportanceofshrinkageinstructuresislargelyrelatedtocracking.Materialshrinkagemaybereducedupto40%,however,bydecreasingtheamountofwaterusedintheoriginalmix.Thisisaccomplishedbyusinghighplasticizingadmixturesallowingforfurtherreductionintheamountofwaterrequired,andbycuringtheconcreteatlowertemperatures,sothatlesswaterisabsorbedintothesurroundingairastheconcretehardens.4.ReinforcedConcreteReinforcedconcreteisbyreasonofitsstrength,durability,availabilityandadaptabilityaneconomicalmaterialeminentlysuitedformanytypesofpermanentstructures.Concreteisrelativelystrongincompressionandcanbemadesufficientlymassivetoprovidelateralstability.Steel,ontheotherhand,isstrongintensionbutoftenlacksadequatelateralstabilityincompressionduetoitsslenderproportions.Areinforcedconcretememberinwhichtheconcreteresistscompression,whilethesteelresiststensionisthereforeanidealstructuralpartnership.Thewidespreaduseofconcreteinengineeringconstructionstemsfromitscheapnesscomparedwithotherstructuralmaterialscurrentlyavailable.Itslackoftensilestrengthisovercomebyincludingreinforcement,usuallyintheformofsteelbars,toproduceacompositematerialknownasreinforcedconcrete.Althoughthesteelreinforcementdoesnotpreventcrackingoftheconcreteinregionsoftension,itdoespreventthecracksfromwidening,anditprovidesaneffectivemeansforresistingtheinternaltensileforces.Thequantityofreinforcementneededisusuallyquitesmall,relativetothevolumeofconcrete,sothatthetotalcostofreinforcedconcreteconstructionremainscommerciallyverycompetitive.Thusarectangulararrangementofverticalandhorizontalsteelbarisintroducedintoregionsofabeamwhereinclinedcrackscanformasaresultofcombinedshearingactionandbendingmoment.Crackinginconcretemaybecausednoton