中英文翻譯橋梁裂縫產(chǎn)生原因淺析近年來，我省交通基礎(chǔ)建設(shè)得到迅猛發(fā)展，各地興建了大量的混凝土橋梁。在橋梁建造和使用過程中，有關(guān)因出現(xiàn)裂縫而影響工程質(zhì)量甚至導(dǎo)橋梁垮塌的報(bào)道屢見不鮮?；炷灵_裂可以說是“常發(fā)病”和“多發(fā)病”，經(jīng)常困擾著橋梁工程技術(shù)人員。其實(shí)，如果采取一定的設(shè)計(jì)和施工措施，很多裂縫是可以克服和控制的。為了進(jìn)一步加強(qiáng)對(duì)混凝土橋梁裂縫的認(rèn)識(shí)，盡量避免工程中出現(xiàn)危害較大的裂縫，本文盡可能對(duì)混凝土橋梁裂縫的種類和產(chǎn)生的原因作較全面的分析、總結(jié)，以方便設(shè)計(jì)、施工找出控制裂縫的可行辦法，達(dá)到防范于未然的作用?；炷翗蛄毫芽p種類、成因?qū)嶋H上，混凝土結(jié)構(gòu)裂縫的成因復(fù)雜而繁多，甚至多種因素相互影響，但每一條裂縫均有其產(chǎn)生的一種或幾種主要原因?；炷翗蛄毫芽p的種類，就其產(chǎn)生的原因，大致可劃分如下幾種：一、荷載引起的裂縫混凝土橋梁在常規(guī)靜、動(dòng)荷載及次應(yīng)力下產(chǎn)生的裂縫稱荷載裂縫，歸納起來主要有直接應(yīng)力裂縫、次應(yīng)力裂縫兩種。直接應(yīng)力裂縫是指外荷載引起的直接應(yīng)力產(chǎn)生的裂縫。裂縫產(chǎn)生的原因有：1、設(shè)計(jì)計(jì)算階段，結(jié)構(gòu)計(jì)算時(shí)不計(jì)算或部分漏算；計(jì)算模型不合理；結(jié)構(gòu)受力假設(shè)與實(shí)際受力不符；荷載少算或漏算；內(nèi)力與配筋計(jì)算錯(cuò)誤；結(jié)構(gòu)安全系數(shù)不夠。結(jié)構(gòu)設(shè)計(jì)時(shí)不考慮施工的可能性；設(shè)計(jì)斷面不足；鋼筋設(shè)置偏少或布置錯(cuò)誤；結(jié)構(gòu)剛度不足；構(gòu)造處理不當(dāng)；設(shè)計(jì)圖紙交代不清等。2、施工階段，不加限制地堆放施工機(jī)具、材料；不了解預(yù)制結(jié)構(gòu)結(jié)構(gòu)受力特點(diǎn)，隨意翻身、起吊、運(yùn)輸、安裝；不按設(shè)計(jì)圖紙施工，擅自更改結(jié)構(gòu)施工順序，改變結(jié)構(gòu)受力模式；不對(duì)結(jié)構(gòu)做機(jī)器振動(dòng)下的疲勞強(qiáng)度驗(yàn)算等。3、使用階段，超出設(shè)計(jì)載荷的重型車輛過橋；受車輛、船舶的接觸、撞擊；發(fā)生大風(fēng)、大雪、地震、爆炸等。次應(yīng)力裂縫是指由外荷載引起的次生應(yīng)力產(chǎn)生裂縫。裂縫產(chǎn)生的原因有：1、在設(shè)計(jì)外荷載作用下，由于結(jié)構(gòu)物的實(shí)際工作狀態(tài)同常規(guī)計(jì)算有出入或計(jì)算不考慮，從而在某些部位引起次應(yīng)力導(dǎo)致結(jié)構(gòu)開裂。例如兩鉸拱橋拱腳設(shè)計(jì)時(shí)常采用布置“X”形鋼筋、同時(shí)削減該處斷面尺寸的辦法設(shè)計(jì)鉸，理論計(jì)算該處不會(huì)存在彎矩，但實(shí)際該鉸仍然能夠抗彎，以至出現(xiàn)裂縫而導(dǎo)致鋼筋銹蝕。2、橋梁結(jié)構(gòu)中經(jīng)常需要鑿槽、開洞、設(shè)置牛腿等，在常規(guī)計(jì)算中難以用準(zhǔn)確的圖式進(jìn)行模擬計(jì)算，一般根據(jù)經(jīng)驗(yàn)設(shè)置受力鋼筋。研究表明，受力構(gòu)件挖孔后，力流將產(chǎn)生繞射現(xiàn)象，在孔洞附近密集，產(chǎn)生巨大的應(yīng)力集中。在長(zhǎng)跨預(yù)應(yīng)力連續(xù)梁中，經(jīng)常在跨內(nèi)根據(jù)截面內(nèi)力需要截?cái)噤撌?，設(shè)置錨頭，而在錨固斷面附近經(jīng)常可以看到裂縫。因此，若處理不當(dāng)，在這些結(jié)構(gòu)的轉(zhuǎn)角處或構(gòu)件形狀突變處、受力鋼筋截?cái)嗵幦菀壮霈F(xiàn)裂縫。實(shí)際工程中，次應(yīng)力裂縫是產(chǎn)生荷載裂縫的最常見原因。次應(yīng)力裂縫多屬?gòu)埨?、劈裂、剪切性質(zhì)。次應(yīng)力裂縫也是由荷載引起，僅是按常規(guī)一般不計(jì)算，但隨著現(xiàn)代計(jì)算手段的不斷完善，次應(yīng)力裂縫也是可以做到合理驗(yàn)算的。例如現(xiàn)在對(duì)預(yù)應(yīng)力、徐變等產(chǎn)生的二次應(yīng)力，不少平面桿系有限元程序均可正確計(jì)算，但在40年前卻比較困難。在設(shè)計(jì)上，應(yīng)注意避免結(jié)構(gòu)突變（或斷面突變），當(dāng)不能回避時(shí)，應(yīng)做局部處理，如轉(zhuǎn)角處做圓角，突變處做成漸變過渡，同時(shí)加強(qiáng)構(gòu)造配筋，轉(zhuǎn)角處增配斜向鋼筋，對(duì)于較大孔洞有條件時(shí)可在周邊設(shè)置護(hù)邊角鋼。荷載裂縫特征依荷載不同而異呈現(xiàn)不同的特點(diǎn)。這類裂縫多出現(xiàn)在受拉區(qū)、受剪區(qū)或振動(dòng)嚴(yán)重部位。但必須指出，如果受壓區(qū)出現(xiàn)起皮或有沿受壓方向的短裂縫，往往是結(jié)構(gòu)達(dá)到承載力極限的標(biāo)志，是結(jié)構(gòu)破壞的前兆，其原因往往是截面尺寸偏小。根據(jù)結(jié)構(gòu)不同受力方式，產(chǎn)生的裂縫特征如下：1、中心受拉。裂縫貫穿構(gòu)件橫截面，間距大體相等，且垂直于受力方向。采用螺紋鋼筋時(shí)，裂縫之間出現(xiàn)位于鋼筋附近的次裂縫。2、中心受壓。沿構(gòu)件出現(xiàn)平行于受力方向的短而密的平行裂縫。3、受彎。彎矩最大截面附近從受拉區(qū)邊沿開始出現(xiàn)與受拉方向垂直的裂縫，并逐漸向中和軸方向發(fā)展。采用螺紋鋼筋時(shí)，裂縫間可見較短的次裂縫。當(dāng)結(jié)構(gòu)配筋較少時(shí)，裂縫少而寬，結(jié)構(gòu)可能發(fā)生脆性破壞。4、大偏心受壓。大偏心受壓和受拉區(qū)配筋較少的小偏心受壓構(gòu)件，類似于受彎構(gòu)件。5、小偏心受壓。小偏心受壓和受拉區(qū)配筋較多的大偏心受壓構(gòu)件，類似于中心受壓構(gòu)件。6、受剪。當(dāng)箍筋太密時(shí)發(fā)生斜壓破壞，沿梁端腹部出現(xiàn)大于45°方向的斜裂縫；當(dāng)箍筋適當(dāng)時(shí)發(fā)生剪壓破壞，沿梁端中下部出現(xiàn)約45°方向相互平行的斜裂縫。7、受扭。構(gòu)件一側(cè)腹部先出現(xiàn)多條約45°方向斜裂縫，并向相鄰面以螺旋方向展開。8、受沖切。沿柱頭板內(nèi)四側(cè)發(fā)生約45°方向斜面拉裂，形成沖切面。9、局部受壓。在局部受壓區(qū)出現(xiàn)與壓力方向大致平行的多條短裂縫。二、溫度變化引起的裂縫混凝土具有熱脹冷縮性質(zhì)，當(dāng)外部環(huán)境或結(jié)構(gòu)內(nèi)部溫度發(fā)生變化，混凝土將發(fā)生變形，若變形遭到約束，則在結(jié)構(gòu)內(nèi)將產(chǎn)生應(yīng)力，當(dāng)應(yīng)力超過混凝土抗拉強(qiáng)度時(shí)即產(chǎn)生溫度裂縫。在某些大跨徑橋梁中，溫度應(yīng)力可以達(dá)到甚至超出活載應(yīng)力。溫度裂縫區(qū)別其它裂縫最主要特征是將隨溫度變化而擴(kuò)張或合攏。引起溫度變化主要因素有：1、年溫差。一年中四季溫度不斷變化，但變化相對(duì)緩慢，對(duì)橋梁結(jié)構(gòu)的影響主要是導(dǎo)致橋梁的縱向位移，一般可通過橋面伸縮縫、支座位移或設(shè)置柔性墩等構(gòu)造措施相協(xié)調(diào)，只有結(jié)構(gòu)的位移受到限制時(shí)才會(huì)引起溫度裂縫，例如拱橋、剛架橋等。我國(guó)年溫差一般以一月和七月月平均溫度的作為變化幅度?？紤]到混凝土的蠕變特性，年溫差內(nèi)力計(jì)算時(shí)混凝土彈性模量應(yīng)考慮折減。2、日照。橋面板、主梁或橋墩側(cè)面受太陽(yáng)曝曬后，溫度明顯高于其它部位，溫度梯度呈非線形分布。由于受到自身約束作用，導(dǎo)致局部拉應(yīng)力較大，出現(xiàn)裂縫。日照和下述驟然降溫是導(dǎo)致結(jié)構(gòu)溫度裂縫的最常見原因。3、驟然降溫。突降大雨、冷空氣侵襲、日落等可導(dǎo)致結(jié)構(gòu)外表面溫度突然下降，但因內(nèi)部溫度變化相對(duì)較慢而產(chǎn)生溫度梯度。日照和驟然降溫內(nèi)力計(jì)算時(shí)可采用設(shè)計(jì)規(guī)范或參考實(shí)橋資料進(jìn)行，混凝土彈性模量不考慮折減。4、水化熱。出現(xiàn)在施工過程中，大體積混凝土（厚度超過2.0米）澆筑之后由于水泥水化放熱，致使內(nèi)部溫度很高，內(nèi)外溫差太大，致使表面出現(xiàn)裂縫。施工中應(yīng)根據(jù)實(shí)際情況，盡量選擇水化熱低的水泥品種，限制水泥單位用量，減少骨料入模溫度，降低內(nèi)外溫差，并緩慢降溫，必要時(shí)可采用循環(huán)冷卻系統(tǒng)進(jìn)行內(nèi)部散熱，或采用薄層連續(xù)澆筑以加快散熱。5、蒸汽養(yǎng)護(hù)或冬季施工時(shí)施工措施不當(dāng)，混凝土驟冷驟熱，內(nèi)外溫度不均，易出現(xiàn)裂縫。6、預(yù)制T梁之間橫隔板安裝時(shí)，支座預(yù)埋鋼板與調(diào)平鋼板焊接時(shí)，若焊接措施不當(dāng)，鐵件附近混凝土容易燒傷開裂。采用電熱張拉法張拉預(yù)應(yīng)力構(gòu)件時(shí)，預(yù)應(yīng)力鋼材溫度可升高至350℃，混凝土構(gòu)件也容易開裂。試驗(yàn)研究表明，由火災(zāi)等原因引起高溫?zé)齻幕炷翉?qiáng)度隨溫度的升高而明顯降低，鋼筋與混凝土的粘結(jié)力隨之下降，混凝土溫度達(dá)到300℃后抗拉強(qiáng)度下降50%，抗壓強(qiáng)度下降60%，光圓鋼筋與混凝土的粘結(jié)力下降80%；由于受熱，混凝土體內(nèi)游離水大量蒸發(fā)也可產(chǎn)生急劇收縮。三、收縮引起的裂縫在實(shí)際工程中，混凝土因收縮所引起的裂縫是最常見的。在混凝土收縮種類中，塑性收縮和縮水收縮（干縮）是發(fā)生混凝土體積變形的主要原因，另外還有自生收縮和炭化收縮。塑性收縮。發(fā)生在施工過程中、混凝土澆筑后4~5小時(shí)左右，此時(shí)水泥水化反應(yīng)激烈，分子鏈逐漸形成，出現(xiàn)泌水和水分急劇蒸發(fā)，混凝土失水收縮，同時(shí)骨料因自重下沉，因此時(shí)混凝土尚未硬化，稱為塑性收縮。塑性收縮所產(chǎn)生量級(jí)很大，可達(dá)1%左右。在骨料下沉過程中若受到鋼筋阻擋，便形成沿鋼筋方向的裂縫。在構(gòu)件豎向變截面處如T梁、箱梁腹板與頂?shù)装褰唤犹?，因硬化前沉?shí)不均勻?qū)l(fā)生表面的順腹板方向裂縫。為減小混凝土塑性收縮，施工時(shí)應(yīng)控制水灰比，避免過長(zhǎng)時(shí)間的攪拌，下料不宜太快，振搗要密實(shí)，豎向變截面處宜分層澆筑。縮水收縮（干縮）。混凝土結(jié)硬以后，隨著表層水分逐步蒸發(fā)，濕度逐步降低，混凝土體積減小，稱為縮水收縮（干縮）。因混凝土表層水分損失快，內(nèi)部損失慢，因此產(chǎn)生表面收縮大、內(nèi)部收縮小的不均勻收縮，表面收縮變形受到內(nèi)部混凝土的約束，致使表面混凝土承受拉力，當(dāng)表面混凝土承受拉力超過其抗拉強(qiáng)度時(shí)，便產(chǎn)生收縮裂縫。混凝土硬化后收縮主要就是縮水收縮。如配筋率較大的構(gòu)件（超過3%），鋼筋對(duì)混凝土收縮的約束比較明顯，混凝土表面容易出現(xiàn)龜裂裂紋。自生收縮。自生收縮是混凝土在硬化過程中，水泥與水發(fā)生水化反應(yīng)，這種收縮與外界濕度無關(guān)，且可以是正的（即收縮，如普通硅酸鹽水泥混凝土），也可以是負(fù)的（即膨脹，如礦渣水泥混凝土與粉煤灰水泥混凝土）。炭化收縮。大氣中的二氧化碳與水泥的水化物發(fā)生化學(xué)反應(yīng)引起的收縮變形。炭化收縮只有在濕度50%左右才能發(fā)生，且隨二氧化碳的濃度的增加而加快。炭化收縮一般不做計(jì)算?；炷潦湛s裂縫的特點(diǎn)是大部分屬表面裂縫，裂縫寬度較細(xì)，且縱橫交錯(cuò)，成龜裂狀，形狀沒有任何規(guī)律。研究表明，影響混凝土收縮裂縫的主要因素有：1、水泥品種、標(biāo)號(hào)及用量。礦渣水泥、快硬水泥、低熱水泥混凝土收縮性較高，普通水泥、火山灰水泥、礬土水泥混凝土收縮性較低。另外水泥標(biāo)號(hào)越低、單位體積用量越大、磨細(xì)度越大，則混凝土收縮越大，且發(fā)生收縮時(shí)間越長(zhǎng)。例如，為了提高混凝土的強(qiáng)度，施工時(shí)經(jīng)常采用強(qiáng)行增加水泥用量的做法，結(jié)果收縮應(yīng)力明顯加大。2、骨料品種。骨料中石英、石灰?guī)r、白云巖、花崗巖、長(zhǎng)石等吸水率較小、收縮性較低；而砂巖、板巖、角閃巖等吸水率較大、收縮性較高。另外骨料粒徑大收縮小，含水量大收縮越大。3、水灰比。用水量越大，水灰比越高，混凝土收縮越大。4、外摻劑。外摻劑保水性越好，則混凝土收縮越小。5、養(yǎng)護(hù)方法。良好的養(yǎng)護(hù)可加速混凝土的水化反應(yīng)，獲得較高的混凝土強(qiáng)度。養(yǎng)護(hù)時(shí)保持濕度越高、氣溫越低、養(yǎng)護(hù)時(shí)間越長(zhǎng)，則混凝土收縮越小。蒸汽養(yǎng)護(hù)方式比自然養(yǎng)護(hù)方式混凝土收縮要小。6、外界環(huán)境。大氣中濕度小、空氣干燥、溫度高、風(fēng)速大，則混凝土水分蒸發(fā)快，混凝土收縮越快。7、振搗方式及時(shí)間。機(jī)械振搗方式比手工搗固方式混凝土收縮性要小。振搗時(shí)間應(yīng)根據(jù)機(jī)械性能決定，一般以5~15s/次為宜。時(shí)間太短，振搗不密實(shí)，形成混凝土強(qiáng)度不足或不均勻；時(shí)間太長(zhǎng)，造成分層，粗骨料沉入底層，細(xì)骨料留在上層，強(qiáng)度不均勻，上層易發(fā)生收縮裂縫。對(duì)于溫度和收縮引起的裂縫，增配構(gòu)造鋼筋可明顯提高混凝土的抗裂性，尤其是薄壁結(jié)（壁厚20~60cm）。構(gòu)造上配筋宜優(yōu)先采用小直徑鋼筋(φ8~φ14)、小間距布置(@10~@15cm)，全截面構(gòu)造配筋率不宜低于0.3%，一般可采用0.3%~0.5%。四、地基礎(chǔ)變形引起的裂縫由于基礎(chǔ)豎向不均勻沉降或水平方向位移，使結(jié)構(gòu)中產(chǎn)生附加應(yīng)力，超出混凝土結(jié)構(gòu)的抗拉能力，導(dǎo)致結(jié)構(gòu)開裂?；A(chǔ)不均勻沉降的主要原因有：1、地質(zhì)勘察精度不夠、試驗(yàn)資料不準(zhǔn)。在沒有充分掌握地質(zhì)情況就設(shè)計(jì)、施工，這是造成地基不均勻沉降的主要原因。比如丘陵區(qū)或山嶺區(qū)橋梁，勘察時(shí)鉆孔間距太遠(yuǎn)，而地基巖面起伏又大，勘察報(bào)告不能充分反映實(shí)際地質(zhì)情況。2、地基地質(zhì)差異太大。建造在山區(qū)溝谷的橋梁，河溝處的地質(zhì)與山坡處變化較大，河溝中甚至存在軟弱地基，地基土由于不同壓縮性引起不均勻沉降。3、結(jié)構(gòu)荷載差異太大。在地質(zhì)情況比較一致條件下，各部分基礎(chǔ)荷載差異太大時(shí)，有可能引起不均勻沉降，例如高填土箱形涵洞中部比兩邊的荷載要大，中部的沉降就要比兩邊大，箱涵可能開裂。4、結(jié)構(gòu)基礎(chǔ)類型差別大。同一聯(lián)橋梁中，混合使用不同基礎(chǔ)如擴(kuò)大基礎(chǔ)和樁基礎(chǔ)，或同時(shí)采用樁基礎(chǔ)但樁徑或樁長(zhǎng)差別大時(shí)，或同時(shí)采用擴(kuò)大基礎(chǔ)但基底標(biāo)高差異大時(shí)，也可能引起地基不均勻沉降。5、分期建造的基礎(chǔ)。在原有橋梁基礎(chǔ)附近新建橋梁時(shí)，如分期修建的高速公路左右半幅橋梁，新建橋梁荷載或基礎(chǔ)處理時(shí)引起地基土重新固結(jié)，均可能對(duì)原有橋梁基礎(chǔ)造成較大沉降。6、地基凍脹。在低于零度的條件下含水率較高的地基土因冰凍膨脹；一旦溫度回升，凍土融化，地基下沉。因此地基的冰凍或融化均可造成不均勻沉降。7、橋梁基礎(chǔ)置于滑坡體、溶洞或活動(dòng)斷層等不良地質(zhì)時(shí)，可能造成不均勻沉降。8、橋梁建成以后，原有地基條件變化。大多數(shù)天然地基和人工地基浸水后，尤其是素填土、黃土、膨脹土等特殊地基土，土體強(qiáng)度遇水下降，壓縮變形加大。在軟土地基中，因人工抽水或干旱季節(jié)導(dǎo)致地下水位下降，地基土層重新固結(jié)下沉，同時(shí)對(duì)基礎(chǔ)的上浮力減小，負(fù)摩阻力增加，基礎(chǔ)受荷加大。有些橋梁基礎(chǔ)埋置過淺，受洪水沖刷、淘挖，基礎(chǔ)可能位移。地面荷載條件的變化，如橋梁附近因塌方、山體滑坡等原因堆置大量廢方、砂石等，橋址范圍土層可能受壓縮再次變形。因此，使用期間原有地基條件變化均可能造成不均勻沉降。對(duì)于拱橋等產(chǎn)生水平推力的結(jié)構(gòu)物，對(duì)地質(zhì)情況掌握不夠、設(shè)計(jì)不合理和施工時(shí)破壞了原有地質(zhì)條件是產(chǎn)生水平位移裂縫的主要原因。喝Thebr家idgec輸rackp忙roduce怕dthe乞reason慈tosi召mplya張nalyse委Inrec拾entye婚ars,t府hetra擇fficc加apital淘const帆ructio槳nofo蛾urpro鐮vince步getss績(jī)wifta指ndvio謠lentd繳evelop陪ment,呆allpa療rtsha今vebui孩ltal扛argen誼umber乒ofcon裂crete哭bridge胡s.In行theco廁urseo炎fbuil銅dinga駱ndusi斷ngin法thebr狡idge,兵releva尾ntto燦influe梅ncepr回oject蒸qualit咐ylead蹲o(hù)fco疾mmono玉ccurre秒ncere雪portt黎hatbr妙idgec猜ollaps肯eeven鐵becau任sethe極crack造appea錘rsThe虛concr丑eteca域nbes天aidto伴"oft圓enhav勉eilln翁essco彎mingo憶n"wh麻ilefr樹acturi爐ngand吸"fre崇quentl專y-occu摸rring挎diseas療e",o份ftenp于erplex委bridg壩eengi覽neers艙andte袋c(diǎn)hnici援a(chǎn)ns.I搏nfact牙,if芽takec值ertain哄desig感nand蔑constr泄uction及measu紗re,a祝lotof唇crack劃scan音beove顫rcome千andco床ntroll箭ed.Fo垃rstre絹ngthen北under晉standi斧ngof滑concre葛tebri晚dgecr昨ackfu晶rther,讓isit世preve糠ntpro振jectf鼓romen漁danger匹large躬rcrac閣ktot莖ryone夢(mèng)'sbes棉t,thi申stext把make牢anmor泄eover培allan折alysis霞,sum脊maryt遇oconc虹retek燦indan柱dreas訪onof鹽produc獎(jiǎng)tion,矮bridg浴eofc悼racka槽smuch行aspo燭ssible壤,ino膠rdert際odesi移gn,c杜onstru銹ctand地find休outth悲efeas貼iblem統(tǒng)ethod該which跡contro郵lthe套crack砌,get岡there桐sulto脫ftaki愚ngpre圾cautio紫nsaga族instY使uWeiR晨an.紛Concre猾tebri血dgecr悠ackki講nd,or莊iginc勸auseo匹fform鐮ation繞Infac阻t,the友origi撓ncaus棕eoff蛾ormati呈onof裹theco棗ncrete緒struc璃turec叨racki渾scomp窄licate慢dand瞇variou黨s,eve臉nmany斬kinds描offa娃ctors妻influe惕nceea卻choth放er,b飽uteve島rycra刺ckhas錄itso尋neor插severa渡lkind載sofm皇ainre料asons巧produc怪ed.T拔hekin秤doft草hecon睡crete筋bridge短crack暗,oni額tsrea嫌sonto睜produ外ce,ca劍nroug邪hlydi貧vides撤everal塑kinds曉asfo種llows紀(jì):嶄First,售load簡(jiǎn)thecr蘭ackca軍usedC傭oncret研einr擴(kuò)outine淹quiet膽.得Isit末loadt易o(hù)move崗andc我rackt之hatpr陵oduce畏claim你toloa墨dthe恰crack只under敗theti豎mesof售stres趙sbrid強(qiáng)ge,su雄mming輛uphas唉direc重tstre鞋sscra輔cks,壇twoki劉ndsst基ressc辛racko放ncesm斗ainly.緞Direc伏tstre穴sscra億ckref庫(kù)erto驟outsid虧eload開direc鑼tcrac魔kthat鋼stres賣sprod蔥uceth熟atcau仿se.Th考ereas翅onwhy鑄thec狼rackp蹦roduce桂sisa掙sfoll悼ows,1斬,Desi紫gnthe怪stage鏟ofca巧lculat彼ing,在doesn帳otcal侵culate尸orle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speltheheatincaseofnecessity,oradoptthethinlayerandbuilditinsuccessioninordertoacceleratedispellingtheheat.5,Theconstructionmeasureisimproperatthetimeofsteammaintenanceorthewinterconstruction,theconcreteissuddenandcoldandsuddenandhot,internalandexternaltemperatureisuneven,apttoappearinthecrack.6,PrefabricateTroofbeamhorizontalbafflewhentheinstallation,propupseatburystencilplatewithtransferflatstencilplatewhenweldinginadvance,ifweldmeasuretobeimproper,ironpiecesofnearbyconcreteeasytoisitfracturetoburn.Adoptelectricheatpiecedrawlawpiecedrawprestressingforceatthecomponent,prestressingforcesteeltemperaturecanriseto350degreesCentigrade,theconcretecomponentisapttofracture.Experimentalstudyindicates,arecausedtheintensityofconcretethatthehightemperatureburnstoobviouslyreducewithrisingoftemperaturebysuchreasonsasthefire,etc.,glueingformingthedeclinethereuponofstrengthofreinforcingbarandconcrete,tensilestrengthdropby50%afterconcretetemperaturereaches300degreesCentigrade,compressionstrengthdropsby60%,glueingthestrengthofformingtodropby80%ofonlyroundreinforcingbarandconcrete;Becauseheat,concretebodydissociateinkevaporateandcanproduceandshrinksharplyinalargeamountThirdshrinkthecrackcausedIntheactualproject,itisthemostcommonbecauseconcreteshrinksthecrackcaused.Shrinkkindinconcrete,plasticityshrinkisititshrinks(isitcontracttodo)tobethemainreasonthatthevolumeofconcreteoutofshapehappenstoshrink,shrinkspontaneouslyinadditionandthecharshrink.Plasticityshrink.About4hoursafteritisbuiltthatinthecourseofconstructing,concretehappens,thecementwaterresponseisfierceatthismoment,thestrandtakesshapegradually,secretewaterandmoisturetoevaporatesharply,theconcretedesiccatesandshrinks,itisatthesametimeconductoneselfwithdignitynotsinkingbecauseaggregate,sowhenhardenconcreteyet,itcallplasticityshrink.Theplasticityshrinkproducingamountgradeisverybig,canbeuptoabout1%.Ifstoppedbythereinforcingbarwhiletheaggregatesinks,formthecrackalongthereinforcingbardirection.Ifweb,roofbeamofTandroofbeamofcaseandcarrybaseplatehandoverofficeincomponentverticaltobecomesectionalplace,becausesinktooreallytosuperficialobeyingthewebdirectioncrackwillhappenevenlybeforehardenning.Forreducingconcreteplasticityshrink,itshouldcontrolbywaterdustwhenbeingconstructthan,lastlong-timemixing,unloadingshouldnottooquick,isitisittakecloselyknittosmashtoshake,verticaltobecomesectionalplaceshoulddividelayerbuild.Shrinkandshrink(doandcontract).Aftertheconcreteisformedhard,asthetoplayermoistureisevaporatedprogressively,thehumidityisreducedprogressively,thevolumeofconcreteisreduced,iscalledandshrunktoshrink(doandcontract).Becauseconcretetoplayermoisturelosssoon,itisslowforinsidetolose,producesurfaceshrinkheavy,insideshrinkalightoneeventoshrink,itisoutofshapetorestrainfrombytheinsideconcreteforsurfacetoshrink,causethesurfaceconcretetobearpullingforce,whenthesurfaceconcretebearspullingforcetoexceeditstensilestrength,produceandshrinkthecrack.Theconcretehardensafter-contractiontojustshrinkandshrinkmainly.Suchasmixmusclerateheavycomponent(exceed3%),betweenreinforcingbarandmoreobviousrestraintsrelativelythatconcreteshrink,theconcretesurfaceisapttoappearinthefullofcrackscrackle.Shrinkspontaneously.Spontaneoustoitshrinkstobeconcreteinthecourseofhardenning,cementandwatertakeplaceinkreact,theshrinkwithhavenothingtodobyexternalhumidity,andcanpositive(whethershrink,suchasordinaryportlandcementconcrete),cannegativetoo(whetherexpand,suchasconcrete,concreteofslagcementandcementofflyash).Thecharshrinks.Betweencarbondioxideandhyrateofcementofatmospheretakeplaceoutofshapeshrinkthatchemicalreactioncause.Thecharshrinksandcouldhappenonlyabout50%ofhumidity,andacceleratewithincreaseofthedensityofthecarbondioxide.Thecharshrinksandseldomcalculates.Thecharacteristicthattheconcreteshrinksthecrackisthatthemajoritybelongstothesurfacecrack,thecrackisrelativelydetailedinwidth,andcriss-cross,becomethefullofcracksform,theformdoesnothaveanylaw.Studieshaveshown,influenceconcreteshrinkmainfactorofcrackasfollows,1,Varietyofcement,gradeandconsumption.Slagcement,quick-hardeningcement,low-heatcementconcretecontractivityarerelativelyhigh,ordinarycement,volcanicashcement,aluminacementconcretecontractivityarerelativelylow.Cementgradelowinaddition,unitvolumeconsumptionheavyrubingdetaileddegreeheavy,thentheconcreteshrinksthemoregreatly,andshrinktimeisthelonger.Forexample,inordertoimprovetheintensityoftheconcrete,oftenadoptandincreasethecementconsumptionmethodbyforcewhileconstructing,theresultshrinksthestresstoobviouslystrengthen.2,Varietyofaggregate.Suchabsorbingwaterratesasthequartz,limestone,cloudrock,granite,feldspar,etc.aresmaller,contractivityisrelativelylowintheaggregate;Andsuchabsorbingwaterratesasthesandstone,slate,angleamphibolite,etc.aregreater,contractivityisrelativelyhigh.Aggregategrainsoffoot-pathheavytoshrinklightinaddition,watercontentbigtoshrinkthelarger.3,Watergraythan.Theheavierwaterconsumptionis,thehigherwateranddustare,theconcreteshrinksthemoregreatly.4,Mixthepharmaceuticaloutside.Itisthebettertomixpharmaceuticalwater-retainingpropertyoutside,thentheconcreteshrinksthesmaller.5,Maintainthemethod.Waterthatgoodmaintenancecanacceleratetheconcretereacts,obtaintheintensityofhigherconcrete.Keephumidityhigh,lowmaintainingtimetobethelongertemperaturewhenmaintaining,thentheconcreteshrinksthesmaller.Steammaintainwaythanmaintainwayconcreteisittakelighttoshrinknaturall.6,Externalenvironment.Thehumidityislittle,theairdrying,temperaturearehigh,thewindspeedislargeintheatmosphere,thentheconcretemoistureisevaporatedfast,theconcreteshrinksthefaster.7,Shakeandsmashthewayandtime.Machineryshakewayofsmashingthanmakefirmbyrammingortampingwayconcretecontractivitytakelittlebyhand.Shakingshoulddetermineaccordingtomechanicalperformancetosmashtime,aregenerallysuitablefor55s/time.Itistooshort,shakeandcannotsmashcloselyknit,itisinsufficientornoteveninintensitytoformtheconcrete;Itistoolong,causeanddividestorey,thickaggregatesinkstothegroundfloor,theupperstratathatthedetailedaggregatestays,theintensityisnoteven,theupperstrataincidentshrinkthecrack.Andshrinkthecrackcausedtotemperature,worthyofconstructingthereinforcingbaragainingcanobviouslyimprovetheresistingthesplittingofconcrete,structureofespeciallythinwall(thick200cmofwall).Mixmuscleshouldisitadoptlightdiameterreinforcingbar(8|?construct14|?)tohavepriority,littleintervalassign(whether@10construct@15cm)onconstructing,thewholesectionisitmixmuscletoberateunsuitabletobelowerthan0toconstruct.3%,cangenerallyadopt0.3%~0.5%.Fourth,crackthatcausesoutofshapeofplinthofthegroundBecausefoundationverticaltoeventosubsideorhorizontaldirectiondisplacement,makethestructureproducetheadditionalstress,gobeyondresistingtheabilityofdrawingofconcretestructure,causethestructuretofracture.Theevenmainreasonthatsubsideofthefoundationisasfollows,1,Reconnoitrestheprecisionandisnotenoughfor,testthematerialsinaccuratlyingeology.Designing,constructingwithoutfullygraspingthegeologicalsituation,thisisthemainreasonthatcausethegroundnottosubsideevenly.Suchashillsareaorbridge,districtof