5土木工程外文翻譯外文文獻(xiàn)英文文獻(xiàn)混凝土應(yīng)力試驗(yàn)

1、混凝土應(yīng)力實(shí)驗(yàn)一、實(shí)驗(yàn)介紹直徑很小的鋼纖維用于混凝土結(jié)構(gòu)可以大大的提升混凝土的抗拉承載水平.在一般情況下混凝土中摻鋼纖維的體積比例在 0.2%2.0%之間.在很小比例下,鋼筋混凝土 的張拉響應(yīng)可假設(shè)為不硬化的類型,它有加大單個(gè)裂縫擴(kuò)展性質(zhì)很像無(wú)鋼筋的素混凝 土,鋼纖維對(duì)混凝土開裂之后性能的改善作用更加明顯,可以通過(guò)限制裂縫的開展從而 較大幅度地提升混凝土的韌性.然而它對(duì)其它性質(zhì)的改良很小,因此在正常實(shí)驗(yàn)方法下 如此低得的纖維含量很難難得到鋼纖維混凝土軸拉應(yīng)力一一應(yīng)變曲線的平穩(wěn)段.為了找 到一個(gè)適宜易行的方法來(lái)研究SFRC軸拉性能人們做了很多工作并且有報(bào)告稱可通過(guò)添 加剛性組件方法來(lái)獲得軸拉全曲

2、線.在這篇文章中 我們將用不同類型的纖維來(lái)做鋼筋混凝土的單軸拉伸試驗(yàn).鋼筋混凝土的抗拉特型首鋼纖維的強(qiáng)度和含量影響.另外,在強(qiáng)力作用下,鋼筋混凝土的應(yīng)力一一 應(yīng)變曲線受多種因素的影響.對(duì)纖維混凝土增強(qiáng)機(jī)理進(jìn)行研究,要獲得鋼纖維混凝土的 受拉全過(guò)程曲線,采用軸拉方法最為適宜,但是要在試驗(yàn)方法上作一定改良,并且試驗(yàn) 機(jī)要有足夠的剛度,來(lái)保證試驗(yàn)過(guò)程的穩(wěn)定.眾所周知,在工程實(shí)踐過(guò)程中,由于施工 技術(shù)及經(jīng)濟(jì)條件的限制,SFRC中纖維體積摻率一般不超過(guò)2%,而大局部工程實(shí)例中, 纖維摻量都在1%左右.為此,本文設(shè)計(jì)了軸拉 SFRC材料試驗(yàn),纖維摻量取1%,并采 用不同種類的纖維增強(qiáng)形式,進(jìn)行比照分析.二

3、、實(shí)驗(yàn)內(nèi)容試驗(yàn)在60噸萬(wàn)能試驗(yàn)機(jī)上進(jìn)行.在試驗(yàn)裝置中添加了四個(gè)高強(qiáng)鋼桿以增大試件的 卸載剛度,并通過(guò)在試件兩端添加球錢來(lái)消除試件的初始偏心率.通過(guò)調(diào)節(jié)連接試件和橫梁的四個(gè)高強(qiáng)螺栓來(lái)保證試件的軸心受拉. 試件相對(duì)兩側(cè)面 之間的拉應(yīng)變值之差不得大于其平均值的 15%.當(dāng)鋼纖維摻量很低為零或 0.5%時(shí), 在荷載峰值采用低周反復(fù)加載曲線的外包絡(luò)線來(lái)獲得軸拉應(yīng)力一一應(yīng)變?nèi)€.02.1材料由四種不同類型的鋼纖維用于該試驗(yàn),這些纖維中三種是帶鉤的和一種是光滑 的.試驗(yàn)中所采用的三種混凝土配合比用于研究,見于表一.在基體強(qiáng)度等級(jí)為C60和C80鋼纖維混凝土中分別參加了大連建科院生產(chǎn)的 DK 5型減水劑和瑞

4、士 Sika公司生 產(chǎn)的液體減水劑.這些被用來(lái)研究鋼纖維混凝土的C30,C60,C80混凝土被制成的試件,在標(biāo)準(zhǔn)情況下養(yǎng)護(hù)28天.三種試件的平均強(qiáng)度見于表一.水泥采用大連小野田水泥廠 生產(chǎn)的32.5級(jí)和52.5級(jí)普通硅酸鹽水泥.細(xì)骨料采用細(xì)度模數(shù) 2. 6的河砂.粗骨料采 用520石灰?guī)r碎石.表水泥強(qiáng)度ISO水泥Kg/m3沙的比率u/c沙屈服強(qiáng)度Kg/m3堿水劑Kg/m3壓縮強(qiáng)度MpaC3032.54500.440.366671185一32.07C6052.55000.350.336121223DK-567.59C8052.516000.290.315351191Sika82.962.2、 試

5、件用建筑結(jié)構(gòu)膠將軸拉試件粘貼于兩端的鋼墊板上.22組共110個(gè)試件的具體參數(shù).2.3、 補(bǔ)充經(jīng)過(guò)28天,普通混凝土和鋼纖維混凝土分別被用來(lái)做抗拉強(qiáng)度試驗(yàn).張拉應(yīng)力一一應(yīng)變曲線由此獲得.對(duì)于高強(qiáng)度鋼纖維混凝土諸如抗拉水平等拉伸特性也由此得到.增 強(qiáng)類鋼纖維混凝土比增韌類鋼纖維混凝土的強(qiáng)度平均提升13%;而由根本開裂至裂縫寬度為0.5mm區(qū)間相應(yīng)的應(yīng)變約2000小的斷裂能積分那么顯示：增韌類鋼纖維混凝土比增 強(qiáng)類鋼纖維混凝土的斷裂能平均提升 20%.由表3還可以看出,大局部SFRC第一峰值對(duì) 應(yīng)的極限拉應(yīng)變值與素混凝土相當(dāng),在 100仙左右,這說(shuō)明低含率纖維的摻入對(duì)提升混 凝土的極限拉應(yīng)變作用不很

6、明顯.而增韌類 SFRC第二峰值對(duì)應(yīng)的應(yīng)變那么大大提升,可 達(dá)1000小£由此可知第二峰值的出現(xiàn)大大提升了材料的韌性.DRAMIX型纖維由于長(zhǎng)度是其它三種纖維長(zhǎng)度的2倍,其斷裂韌性更好,在試驗(yàn)曲線中可以看出在應(yīng)變到達(dá)后, 其荷載強(qiáng)度仍然保持較高水平,直到10000H拉變時(shí)荷載仍可保持其峰值水平的 50%左 右.三、試驗(yàn)結(jié)果和分析3.1 劈拉強(qiáng)度和軸拉極限強(qiáng)度不同試件的劈拉強(qiáng)度和軸拉極限強(qiáng)度查表,在混凝土中增加鋼纖維的量可以提升它 的劈拉強(qiáng)度和軸拉極限強(qiáng)度,兩種不同參數(shù)的鋼纖維鋼筋混凝土和普通混凝土它們的 混合比例相同的比率也可查表.3.1.1 基體強(qiáng)度及纖維類型對(duì)軸拉強(qiáng)度的影響從上我

7、們可以看出鋼纖維對(duì)初裂強(qiáng)度的增強(qiáng)作用受基體強(qiáng)度變化的影響很小.也就是說(shuō)在摻人同種鋼纖維時(shí),隨著基體強(qiáng)度的增加,鋼纖維混凝土與同配比素混凝土的初 裂強(qiáng)度的比值根本恒定然而,不同情況下的極限抗拉強(qiáng)度是不一樣的,當(dāng)基體強(qiáng)度增加時(shí),對(duì)于不同類型 的鋼纖維,極限抗拉強(qiáng)度的分配量是不同的.另外它的增加量比劈拉恰強(qiáng)度大F1型鋼纖維作為基體的極限抗拉強(qiáng)度很高,這是由于這類型的鋼纖維的強(qiáng)度很高 大于1100MPa試驗(yàn)過(guò)程中沒(méi)有纖維拔斷的現(xiàn)象出現(xiàn)而且當(dāng)基體強(qiáng)度較高時(shí)C80,鋼纖維的端部彎鉤被完全拉直.由于黏結(jié)強(qiáng)度的提升,基體強(qiáng)度越高,該纖維對(duì)高強(qiáng)混 凝土軸拉極限強(qiáng)度的增強(qiáng)效果越好.F2和F3型鋼纖維的強(qiáng)度較高,二

8、者均有端部彎鉤, 并且外表較為粗糙,當(dāng)基體強(qiáng)度較高時(shí) C80,出現(xiàn)纖維拔斷現(xiàn)象,該現(xiàn)象的出現(xiàn)對(duì)這 兩種鋼纖維的增強(qiáng)效果產(chǎn)生了消極影響,因此為了最大限度的發(fā)揮這兩種鋼纖維的增強(qiáng) 作用,應(yīng)將其應(yīng)用于中高強(qiáng)度混凝土中.F4型纖維為長(zhǎng)直型,其與基體問(wèn)的粘結(jié)力較小,因此它的增強(qiáng)效果耍弱于其他二 種.由于其與基體問(wèn)的粘結(jié)力較小因此在試驗(yàn)過(guò)程中沒(méi)有纖維拔斷現(xiàn)象出現(xiàn).并且隨著 基體強(qiáng)度升高,由于黏結(jié)力的增大,該纖維增強(qiáng)效率有持續(xù)提升.3.1.2 鋼纖維摻量對(duì)軸拉強(qiáng)度的影響試驗(yàn)中重點(diǎn)針對(duì)F3型鋼纖維研究了纖維摻量的變化對(duì)鋼纖維高強(qiáng)混凝土軸拉初裂 強(qiáng)度和極限強(qiáng)度的影響.試驗(yàn)中鋼纖維體積摻率變化范圍為 0.5-1.

9、5o可見隨著纖維摻量 增大,軸拉初裂強(qiáng)度和極限強(qiáng)度均有提升.兩圖中曲線的上升趨勢(shì)很相似.也就是說(shuō)纖 維摻量在整個(gè)拉伸過(guò)程中對(duì)鋼纖維混凝土內(nèi)拉應(yīng)力的影響是積極的和穩(wěn)定的.纖維序號(hào)F10.642F20.862F30.794F40.589鋼纖維鋼筋混凝土軸拉極限強(qiáng)度可以用下式來(lái)計(jì)算:A "+ 口武D式中：fft為鋼纖維鋼纖維軸拉極限強(qiáng)度軸拉極限強(qiáng)度；ft為同配比素混凝土軸拉極限強(qiáng)度；纖維類型系數(shù)有表四給出1 ./為鋼纖維體積摻率,l/d為鋼纖維長(zhǎng)徑比.勺二四不,/3.2 軸拉變形性能和韌性3.2.1 初裂拉應(yīng)變和峰值荷載拉應(yīng)變對(duì)試件四周四個(gè)夾式位移計(jì)測(cè)得的應(yīng)變值進(jìn)行平均獲得試件的拉應(yīng)變值.

10、假設(shè)試驗(yàn)中試件相對(duì)側(cè)面的拉應(yīng)變差大于平均值的15%,該試件作廢.高強(qiáng)SFRC的初裂拉應(yīng)變和峰值拉應(yīng)變要遠(yuǎn)大于同配比素混凝土見表5,隨著基體強(qiáng)度或者纖維摻量增大,這個(gè)差值有所增長(zhǎng),鋼纖維對(duì)峰值應(yīng)變的提升作用要比初裂 應(yīng)變更加明顯.3.2.2 拉伸功和軸拉韌性指數(shù)拉伸功為位移0-0. 5 mm軸拉荷載位移全曲線下面積圖5中陰影面積.另外,引 入軸拉韌性指數(shù).其定義為：式中:fft為鋼纖維混凝土軸拉極限強(qiáng)度；A為軸拉試件的破壞橫截面面積.兩參數(shù)均用來(lái)評(píng)價(jià)鋼纖維高強(qiáng)混凝土在軸拉過(guò)程中的韌性.軸拉韌性指數(shù)為無(wú)量綱 系數(shù),與軸拉功相比,在評(píng)價(jià)軸拉韌性時(shí)可在一定程度上消除軸拉極限強(qiáng)度的差異所帶 來(lái)的影響.從

11、上我們可以發(fā)現(xiàn),基體強(qiáng)度和纖維含量?jī)煞N參數(shù)的有規(guī)律的改變很相似,因此我 們分析的重點(diǎn)應(yīng)放在韌性指數(shù)上.摻有四種鋼纖維及素混凝土試件基體強(qiáng)度與軸拉韌性指數(shù)的關(guān)系成比例, 其中纖維 混凝土試件中鋼纖維體積摻率均為 1.0%.可見高強(qiáng)SFRC的軸拉韌性要遠(yuǎn)遠(yuǎn)優(yōu)于同配 比素混凝土.鋼纖維的抗拉強(qiáng)度的影響是顯著的,隨著基體強(qiáng)度升高,混凝土脆性明顯增加,素 混凝土軸拉韌性明顯下降.在摻有 F1和F2型鋼纖維的試件中也出現(xiàn)了韌性下降現(xiàn)象. F1型纖維從基體中拔出其實(shí)是一個(gè)纖維端鉤被拉直,纖維端部周圍混凝土被擠碎的過(guò) 程.當(dāng)纖維端鉤最終被拉直時(shí),軸拉荷載很快下降.混凝土的強(qiáng)度越高,基體硬度和脆 性越大,上述過(guò)

12、程歷時(shí)也更短.因此當(dāng)基體強(qiáng)度較高時(shí),軸拉應(yīng)力一一應(yīng)變曲線下降得更快,軸拉韌性指數(shù)也有所下降.在四種類型纖維種F1型纖維的增韌效果最好,F2型纖維長(zhǎng)徑比最小,基體強(qiáng)度較 高時(shí)出現(xiàn)了纖維拔斷現(xiàn)象,因此當(dāng)基體強(qiáng)度增加時(shí)韌性指數(shù)不斷下降.F3和F4型鋼纖維韌性指數(shù)均隨基體強(qiáng)度升高而增大.這兩種纖維均為剪切型,表 面較粗糙.在鋼纖維和基體之間黏結(jié)力的各組分中,摩擦力起主導(dǎo)作用.摩擦力隨基體 強(qiáng)度的升高而增大,且該黏結(jié)類型的拔出破壞是一個(gè)持續(xù)過(guò)程,因此基體強(qiáng)度升高對(duì)摻 有這兩種鋼纖維的混凝土韌性起積極作用.這兩種纖維的不同之處是F3型的兩端有彎鉤.由于端鉤的存在使得在基體強(qiáng)度不太高時(shí) C30和C60, F

13、3型鋼纖維的增韌作用優(yōu) 于F4型.當(dāng)基體強(qiáng)度很高時(shí)C80,由于纖維拔斷現(xiàn)象影響了 F3型的增韌效果,F4型 鋼纖維的增韌效果叉反過(guò)來(lái)超過(guò)了 F3型鋼纖維.3.3 鋼纖維鋼筋混凝土單軸拉伸應(yīng)力一一應(yīng)變曲線典型的鋼纖維高強(qiáng)混凝土軸拉應(yīng)力一應(yīng)變?nèi)€為了便于比擬,每組試件選出條 典型曲線作為代表,表述了軸拉曲線隨基體強(qiáng)度的變化規(guī)律；表述了軸拉曲線隨鋼纖 維F3型摻量的變化規(guī)律.曲線由彈性階段、彈塑性階段和下降段 軟化段組成.下降 段存在拐點(diǎn).從上中可以看到,基體強(qiáng)度越高,軸拉應(yīng)力一應(yīng)變?nèi)€下降得越快.另外,鋼纖 維摻量的提升可以大大地改善曲線的飽滿程度.鋼纖維類型對(duì)軸拉應(yīng)力一應(yīng)變?nèi)€的 形狀也有

14、一定的影響.Fl型纖維的曲線是幾種鋼纖維中最飽滿的, 并且在拉應(yīng)變?yōu)榇蠹s 10000個(gè)微應(yīng)變時(shí)出現(xiàn)了第二峰值. 該現(xiàn)象表達(dá)了 Fl型纖維良好的增韌效果.當(dāng)基體強(qiáng) 度較高時(shí),由于纖維拔斷的出現(xiàn)使得F2和F3型鋼纖維試件的軸拉曲線下降端呈階梯狀. F4型纖維的曲線較為平滑,形狀與素混凝土曲線相似,但是更為飽滿.這是由于長(zhǎng)直 形鋼纖維的拔出過(guò)程是相對(duì)連續(xù)和柔和的.四、研究分析由4種鋼纖維混凝土的典型拉伸應(yīng)力-應(yīng)變曲線可以看出：在軸拉條件下,1%摻量 的鋼纖維遠(yuǎn)遠(yuǎn)沒(méi)有到達(dá)使混凝土材料實(shí)現(xiàn)應(yīng)變強(qiáng)化的地步,大局部試驗(yàn)曲線都在到達(dá)峰值后,出現(xiàn)荷載驟降段.但是,隨著變形的增加,有兩條曲線有明顯的第二峰值出現(xiàn),

15、 而另外兩條那么沒(méi)有,正是根據(jù)這種現(xiàn)象,可以將其分為增強(qiáng)和增韌兩大類鋼纖維混凝土,有第二峰值的為增韌類,無(wú)第二峰值的為增強(qiáng)類.曾經(jīng)有許多鋼纖維混凝土軸拉應(yīng)力一應(yīng)變?nèi)€模型提出大多數(shù)為分段函數(shù),以應(yīng)力峰值點(diǎn)為分界點(diǎn).本文中,全曲線的上升段和下降段采用不同的函數(shù)表達(dá)式.在公式3中4.1 上升段的公式上升段的數(shù)學(xué)模型為:這里：叫,固和 力為與基體和鋼纖維特性有關(guān)的參數(shù). 邊界條件為：1） X=0, Y=0;2） X=0, dy/dx=E0 /Ep；3X=1 , Y=1 , dy/dx=0.由邊界條件可得公式5可以簡(jiǎn)化為： = . 5四系數(shù) 可以通過(guò)試驗(yàn)數(shù)據(jù)回歸獲得6a I = 0x33式中：E0為

16、圓點(diǎn)切線模量；EP為峰值應(yīng)力點(diǎn)割線模量第一峰值 因此公式6可以轉(zhuǎn)換為：x：二 u仁4.2下降段公式下降段數(shù)學(xué)的模型為:式中：八和''為與基體和鋼纖維特性有關(guān)的參數(shù).(8)下降段表達(dá)式中系數(shù)值選取1.7.邊界條件x=l和y=1自然滿足.系數(shù)的取值通過(guò) 最小二乘法回歸獲得：町=0.22 x/：? x (1 + 尤廣(9)可見基體強(qiáng)度和纖維參量對(duì)軸拉曲線下降段的下降速率的影響是相反的.五、理論曲線與試驗(yàn)結(jié)果的比擬鋼纖維高強(qiáng)混凝土軸拉應(yīng)力一應(yīng)變理論曲線和試驗(yàn)曲線的比擬如圖12所示(以試件F36010為例).可見,理論結(jié)果與試驗(yàn)結(jié)果符合較好.六、實(shí)驗(yàn)結(jié)論(1)試驗(yàn)結(jié)果說(shuō)明：鋼纖維高強(qiáng)混凝

17、土劈拉強(qiáng)度略高于軸拉強(qiáng)度,兩者有較好的相關(guān)性,鋼纖維高強(qiáng)混凝土軸拉強(qiáng)度可取為劈拉強(qiáng)度的 0.9倍.(2)在摻入同種同量鋼纖維時(shí),隨著基體強(qiáng)度的增加,鋼纖維高強(qiáng)混凝土與同配比素 混凝土的初裂強(qiáng)度的比值根本不變；軸拉極限強(qiáng)度的比值有所變化,且該變化對(duì)不同的 纖維類型有所不同,鋼纖維與基體黏結(jié)性能好,且破壞時(shí)不被拉斷,那么增強(qiáng)效果好.(3)提升鋼纖維摻量對(duì)鋼纖維高強(qiáng)混凝土的抗拉強(qiáng)度特性的改善作用比對(duì)普通強(qiáng)度 混凝土的改善作用明顯.(4)鋼纖維高強(qiáng)混凝土的初裂應(yīng)變和峰值應(yīng)變要比素混凝土的增幅隨基體強(qiáng)度和纖 維摻量的升高而增大.(5)引入了軸拉韌性指數(shù)來(lái)評(píng)價(jià)鋼纖維高強(qiáng)混凝土的韌性,鋼纖維混凝土的軸拉韌性

18、 要大大優(yōu)于同配比的索混凝土,并且受基體強(qiáng)度和鋼纖維特性和摻量的影響.(6)基體強(qiáng)度越高,鋼纖維高強(qiáng)混凝土的軸拉應(yīng)力應(yīng)變曲線在峰值過(guò)后下降得越快； 纖維摻量的提升可以大大改善曲線的飽滿程度,鋼纖維類型對(duì)曲線形狀也有一定的影 響.通過(guò)對(duì)實(shí)驗(yàn)曲線的分析與回歸,給出了考慮上述影響因素的鋼纖維高強(qiáng)混凝土軸拉 應(yīng)力應(yīng)變?nèi)€表達(dá)式.(7)綜合而言,四種鋼纖維中,F3型鋼纖維的增強(qiáng)效果最好,而 F1型鋼纖維的增韌 效果最好.外文譯原文Concrete stress test 1 Test IntroductionThe tensile properties of concrete can be enhan

19、ced substantially by incorporating high strength and small diameter short steel fibers, which leads to the steel fiber reinforced concrete(SFRC). In conventional SFRC, the steel fiber content is usually within the range of 0. 2%2% by volume. At such a low 6her content, the tensile response of SFRC w

20、ould assume a nonhardening typewhich is characterized by the widening of a single crack similar to an unreinforced concrete . The contribution of fibers is apparent in the post cracking response, represented by an increase inpost： cracking ductility due to the work associated with pullout of fibers

21、bridging a failure crack. However, improvements in some other properties are insignificant . Moreover, the softening segment of the stress strain curve of SFRC with such a low fiber content under uniaxial tension is difficult to be got with normalexperimental methods Many works have been done to fin

22、d a suitable and relatively easy way to analyze the tensile characteristics . And it was reported that the whole curve could be got on a normal testing machine with stiffening components added.In this article, the stress strain behavior of SFRC under uniaxial tension Was analyzed for different types

23、 of fiber. The tensile characteristics of SFRC influenced by the matrix strength and the steel fiber content were studied alsoIn addition , the stress-strain curves of high strength SFRC with different factors were well acquired. The mechanism of fiber reinforced concrete to enhance research, to obt

24、ain steel fiber reinforced concrete in tension curve of the whole process, using the most appropriate method of axial tension, but to make sure the testing methods improved, and the testing machine must have enough stiffness to ensure the testing process stability. Is well known in engineering pract

25、ice, process, technology and economic conditions due to construction constraints, SFRC-doped fiber volume in the rate of generally not more than 2%, while most of the engineering example, the fiber fraction are about 1%. In this paper the design of the axial tension SFRC material testing, fiber dosa

26、ge to take 1%, and using different types of fiber-reinforced forms, were analyzed.2 Experimental ContentThe specimens were tested on a 60 kN universal testing machine Four high steel bars were added to enhance the stiffness of the testing machine In addition, spherichinges were used to abate the ini

27、tial axial eccentricity of the specimen s.It was ensured that specimens should be pulled under uniaxial tension by adjusting the four high strength bolts which connect the specimens to the crossbeam. And the difference between the tensile strains of the opposite sides of the specimen should be less

28、than 1 % of their mean value. When the fiber content was low (0 and 0.% by volume), the cyclic quire the whole stress strain.2. 1 MaterialsFour types of steel fibers shown in Table were chosen for this test Three of these fibers (F1, F2 and F3) were hooked-end and the other one(F4)was smoothThree co

29、ncrete mixtures shown in Table 2, were investigated. Water reducing agents were used in C60 and C80 mixes(DK - 5 made by Dalian Structure Research Institute and Sika made in Switzerland respectively). The compressive strengths of these C3,0 C60, C80 mixes were determined according to “TestMethods Us

30、ed for Steel Fiber Reinforced Concrete "(CECS ：1超9)"8 3 at 28 days using 150 mm150 mm M50 mm cube s Averaged results for 3 specimens are given in Table 2. 0rdinary Portland cement(yielded by Dalian Huaneng Onoda Cement Company)of 32. 5 and 52. 5 (according to China standard) were chosen .

31、River sand(modulus of fineness is 2.6)and crushed limestone coarse aggregates" 20 Bin) were usedTableMatrix codeStrength grade Of cement (ISO)Cement Kg/m3u/cratioSand ratioSandKg/m3CrushedStrneKg/m3Water reducingCompressiveStrengthMpaC3032.54500.440.36667115537.07C6052.55000.350.336021223DK-567

32、.59C8052.56000.290.315351190Sika82.962. 2 SpecimenThe tensile specimen was bonded to steel padding plates at both ends by tygoweldA total of 1 1 0 specimens were divided into 22 groups according to certain parametersThe parameters of these specimens are shown in Table .3 2. 3 ItemsAt the age of 28 d

33、ays, plain concrete and steel fiber concrete specimens were tested for tensile strength, respectively .The tensile stress strain curves were acquired. Many other tensile characters of the high strength steel fiber concrete such as tensile work , etc were calculated also. Enhanced class steel fiber r

34、einforced concrete toughness category than the strength of steel fiber reinforced concrete an average of 13%; while cracking from the basic to the crack width of 0.5mm interval (the corresponding strain of about 2000 仙 esh owed the fracture energy integral: toughening class steel fiber reinforced co

35、ncrete enhanced class than the fracture energy of steel fiber reinforced concrete an average of 20%. from Table 3 also shows that most of the SFRC first peak correspondsto the limit of tensile strain value and plain concrete rather, in the 100 仙 earound, indicating a low rate of fiber-containing inc

36、orporation in improving the role of ultimate tensile strain of concrete is not very obvious. The toughening class SFRC second peak coesponds to a much greater strain, up to 1000以 £From this second peak has greatly enhancedthe appearanceof toughness. DRAMIX Fiber because of the length of other t

37、hree kinds of fiber length of 2 times the fracture toughness and better in the test curve can be seen in the strain is attained, the load continues to maintain a high level of intensity, until the strain when the load so as to maintain 10000仙 8of 50%.3 Results and Discussion3. 1 Crack stress and ult

38、imate tensile strengthThe crack stress and ultimate tensile strength of different specimens are listed in Table 3. The addition of steel fibers into concrete increased its crack stress an d ultimate tensile strength. And the ratios of these two parameters of SFRC to those of plain concreue (with the

39、 same mix proportion)are given in Table 3 too.3. 1 . 1 Effect of matrix strength an(1 fiber typeFrom table 3. It can be seen that the effects of steel fibers 0n crack stress are little influenced by the matsix strength . That is to say . When the matrix strength increases, the ratios of crack stress

40、esof SFRC ( with the same type of fibers contained)to those of plain concrete ones with the same mix proportion are invariableHowever, the condition for ultimate tensile strength is different. When the matrix strength increasesthese ratios of ultimate tensile strengths(shown in Table 3)vary dissimil

41、arly according to the type of steel fiber. Moreover, the increments are bigger than those of crack stressThe heightening efficiency of fiber F1 for ultimate tensile strength rises as matrix strength increases It is becausethat the strength of this kind of fiber is very high(>1 100 MPa). No fiber

42、broken was observed during the test and the hooked ends of the fibers were straightened when the matrix strength was high(C80) The higher the matrix strength this kind of steel fiber takes on its strengthening effect more efficiently for the increasing of bond stress The strengths of fibers F2 and F

43、3 are midhigh(>700 MPa). They all have hooked ends and both of their surfaces are coarse When the matrix strength was high(C80) . fiber breaking occurred in the test And this phenomenon impaired the heightening efficiency ofthese two kinds of steel fiber So they should be used in middle strength

44、concrete to exert their strengthening effect more efficiently. Fiber F4 is smooth, and its bond stress with matrix is comparatively low . T1erefore . its strengthening effect is 1ess notable than those of other kinds of fiber. Because of the low bond stress no fiber broken was found during the test

45、and its heightening efficiency for ultimate tensile strength rises as matrix strength increases 3. 1 .2 Effect of fiber contentThe effect of fiber content on the crack stress and u1 . ultimate tensile strength was investigated for SFRC contained fiber F3. And the fiber content varied from 0. 5% to 1

46、 . 5% by volume(shown in Table 3). It can be seen from Fig 1 and Fig. 2 that as the fiber content increasesat0.6420.8620.7940.589The crack stress and ultimate strength of SFRC improve obviouslyMoreover. the rising trends of the curves in these two figures are stupendously similarn other words, the e

47、ffect of fiber content on the characters of tensile stress of SFRC is positive and consistent Table 4 Fiber type factorsFiber codeF1F2F3F4The tensile strength of SFRC can be calculated with the follow formula where, fft is the ultimate tensile strength of SFRC; the ultimate tensile strength of plain

48、 concrete with the same mixing proportion； a, the fiber type factor, 一勺二臼閂which is shown Table 4；is the fiber content 0f volume and l/d is the aspectratio of steel fibers.3. 2 Tensile strain and toughness characters3.2. 1 Crack strain and the strain at peak tensile loadThe tensile strains were acqui

49、red by averaging the readings of the four displacement sensors fixed around the specimen In addition, the specimens whose difference between the tensile strains of its opposite sides is larger than 15 of their mean value were blanked outThe crack strain or the strains at peak tensile load of SFRC ar

50、e much bigger than those of plain concrete(as shown in Table 5). And the increments go up as the matrix strength or the fiber content increases Compared to that on crack strain the increscent effect of steel fiber on the strain at peak tensile load is more remarkable 3. 2. 2 Tensile work and toughne

51、ss modulusThe tensile work was defined as the area under the load-displacement curve from 0 to 0. 5 rain. Moreover, a tensile toughness modulus was introduced(shown in Table 5) It was defined as where, fft is the ultimate tensile strength of SFRC; A, the area of the cross section of specimen.Both th

52、ese two parameters were quoted to evaluate the toughness characters of SFRC under uniaxial tension. The tensile toughness modulus is a dimensionless factorCompared to what the tensile work does it can avoid the influence of the ultimate tensile strength when studying the toughness of SFRCIt call be

53、found from Table 5 that the altering regularities of these two factors along with the changes of matrix strength and fiber content are approximateTherefore, the emphasis of analysis was put on the toughness modulu sThe relationship between the matrix strength and toughness modulus of SFRC with four

54、kinds of steel fiber are shown in Fig . 3. whose fiber contents are all 1 . O % by volume. together with that relationship of plain concrete. The tensile toughness of SFRC is much better than that of plain concrete The tensile toughening effect of steel fiber is remarkable. As the matrix strength ri

55、ses The brittleness of concrete increases obviouslyand then the tensile toughness of plain concrete falls down This phenomenon was also found on specimens containing fiber F1and F2. The pulling out of fiber F1 from concrete is in fact a process of hook-end' seeing straightened and the matrix 

56、9; being crushed around the hook-end When the hooked end is straightened at last the tensile load falls down quickly . The higher the concrete strength. the larger the rigidity of the matrix and the shorter the time that the process mentioned above lastsThus the stress-strain curve falls down more q

57、uickly , and then the toughness modulus decreasesdowever, the toughening effect of fiber F1 is the best among these four kinds of steel fiber The aspect ratio of fiber F2 is the least and when the matrix strength is high, fiber breaking occurs. Therefore, the toughness modulus falls down continually

58、 as the matrix strength rises.The toughness modului of fibers F3 and F4 rise together with the matrix strength Both the two kinds of fiber are snipped and their surfaces are coarse. Therefore, the friction is dominant in the proportions of bond stress Because the friction between fiber and matrix increases along with the matrix strength , and the whole pulling out of these kinds of bond status is a continuous process the