5土木工程外文翻譯外文文獻(xiàn)英文文獻(xiàn)混凝土應(yīng)力實驗

1、混凝土應(yīng)力實驗一、實驗介紹直徑很小的鋼纖維用于混凝土結(jié)構(gòu)可以大大的提高混凝土的抗拉承載能力。在一般情況下混凝土中摻鋼纖維的體積比例在0.22.0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，它有加大單個裂縫擴(kuò)展性質(zhì)很像無鋼筋的素混凝土，鋼纖維對混凝土開裂之后性能的改善作用更加明顯，可以通過控制裂縫的開展從而較大幅度地提高混凝土的韌性。然而它對其它性質(zhì)的改進(jìn)很小，因此在正常實驗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)力應(yīng)變曲線的平穩(wěn)段。為了找到一個合適易行的方法來研究sfrc軸拉性能人們做了很多工作并且有報告稱可通過添加剛性組件方法來獲得軸拉全曲線。在這篇文章中,我們

2、將用不同類型的纖維來做鋼筋混凝土的單軸拉伸試驗。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)力應(yīng)變曲線受多種因素的影響。對纖維混凝土增強(qiáng)機(jī)理進(jìn)行研究，要獲得鋼纖維混凝土的受拉全過程曲線，采用軸拉方法最為適宜，但是要在試驗方法上作一定改進(jìn)，并且試驗機(jī)要有足夠的剛度，來保證試驗過程的穩(wěn)定。眾所周知，在工程實踐過程中，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2%，而大部分工程實例中，纖維摻量都在1%左右。為此，本文設(shè)計了軸拉sfrc材料試驗，纖維摻量取1%，并采用不同種類的纖維增強(qiáng)形式，進(jìn)行對比分析。二、實驗內(nèi)容試驗在60噸萬能試驗機(jī)上進(jìn)行。

3、在試驗裝置中添加了四個高強(qiáng)鋼桿以增大試件的卸載剛度，并通過在試件兩端添加球鉸來消除試件的初始偏心率。通過調(diào)節(jié)連接試件和橫梁的四個高強(qiáng)螺栓來保證試件的軸心受拉。試件相對兩側(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），在荷載峰值采用低周反復(fù)加載曲線的外包絡(luò)線來獲得軸拉應(yīng)力應(yīng)變?nèi)€.。2.1材料由四種不同類型的鋼纖維用于該試驗，這些纖維中三種是帶鉤的（和）一種是光滑的。試驗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)度等級為c60和c80鋼纖維混凝土中分別加入了大連建科院生產(chǎn)的dk一5型減水劑和瑞士sika公司生產(chǎn)的液體減水劑。這些被用來研究鋼纖維混凝

4、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級和52.5級普通硅酸鹽水泥。細(xì)骨料采用細(xì)度模數(shù)26的河砂。粗骨料采用520 石灰?guī)r碎石。 表一水泥強(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mpac3032.54500.440.36667118532.07c6052.55000.350.336121223dk-567.59c8052.56000.290.315351191sika82.962.2、試件用建筑結(jié)構(gòu)膠將軸拉試件粘貼于兩端的鋼墊板上。22組共110個試件

5、的具體參數(shù)。2.3、補(bǔ)充經(jīng)過28天，普通混凝土和鋼纖維混凝土分別被用來做抗拉強(qiáng)度試驗。張拉應(yīng)力應(yīng)變曲線由此獲得。對于高強(qiáng)度鋼纖維混凝土諸如抗拉能力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)度平均提高13%；而由基本開裂至裂縫寬度為0.5mm區(qū)間(相應(yīng)的應(yīng)變約2000)的斷裂能積分則顯示：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高20%.由表3還可以看出，大部分sfrc第一峰值對應(yīng)的極限拉應(yīng)變值與素混凝土相當(dāng)，在100左右，這說明低含率纖維的摻入對提高混凝土的極限拉應(yīng)變作用不很明顯。而增韌類sfrc第二峰值對應(yīng)的應(yīng)變則大大提高，可達(dá)1000，由此可知第二峰值的出

6、現(xiàn)大大提高了材料的韌性。dramix型纖維因為長度是其它三種纖維長度的2倍，其斷裂韌性更好，在試驗曲線中可以看出在應(yīng)變達(dá)到后，其荷載強(qiáng)度仍然保持較高水平，直到10000應(yīng)變時荷載仍可保持其峰值水平的50%左右。三、試驗結(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高它的劈拉強(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)度及纖維類型對軸拉強(qiáng)度的影響從上我們可以看出鋼纖維對初裂強(qiáng)度的增強(qiáng)作用受基體強(qiáng)度變化的影響很小。也就是說在摻人同種鋼纖維時，隨著基體強(qiáng)度的增加，鋼纖

7、維混凝土與同配比素混凝土的初裂強(qiáng)度的比值基本恒定然而，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，對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，這是因為這類型的鋼纖維的強(qiáng)度很高（大于1100mpa）試驗過程中沒有纖維拔斷的現(xiàn)象出現(xiàn)而且當(dāng)基體強(qiáng)度較高時(c80)，鋼纖維的端部彎鉤被完全拉直。由于黏結(jié)強(qiáng)度的提高，基體強(qiáng)度越高，該纖維對高強(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，二者均有端部彎鉤，并且表面較為粗糙，當(dāng)基體強(qiáng)度較高時(c80)，出現(xiàn)纖維拔斷現(xiàn)象，該現(xiàn)象的出現(xiàn)對這兩種鋼纖維的增強(qiáng)效

8、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型纖維為長直型，其與基體問的粘結(jié)力較小，因此它的增強(qiáng)效果耍弱于其他二種。因為其與基體問的粘結(jié)力較小因此在試驗過程中沒有纖維拔斷現(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)提高。3.1.2鋼纖維摻量對軸拉強(qiáng)度的影響試驗中重點針對f3型鋼纖維研究了纖維摻量的變化對鋼纖維高強(qiáng)混凝土軸拉初裂強(qiáng)度和極限強(qiáng)度的影響。試驗中鋼纖維體積摻率變化范圍為0.5-1.5。可見隨著纖維摻量增大，軸拉初裂強(qiáng)度和極限強(qiáng)度均有提高。兩圖中曲線的上升趨勢很相似。也就是說纖維摻量在整個拉伸過程中對鋼纖維混

9、凝土內(nèi)拉應(yīng)力的影響是積極的和穩(wěn)定的。纖維序號 f1 0.642f2 0.862f3 0.794f4 0.589鋼纖維鋼筋混凝土軸拉極限強(qiáng)度可以用下式來計算： （1）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)有表四給出為鋼纖維體積摻率，l/d 為鋼纖維長徑比。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)變對試件四周四個夾式位移計測得的應(yīng)變值進(jìn)行平均獲得試件的拉應(yīng)變值。若試驗中試件相對側(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

10、，這個差值有所增長，鋼纖維對峰值應(yīng)變的提高作用要比初裂應(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0-05 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： (2)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)均用來評價鋼纖維高強(qiáng)混凝土在軸拉過程中的韌性。軸拉韌性指數(shù)為無量綱系數(shù)，與軸拉功相比，在評價軸拉韌性時可在一定程度上消除軸拉極限強(qiáng)度的差別所帶來的影響。從上我們可以發(fā)現(xiàn)，基體強(qiáng)度和纖維含量兩種參數(shù)的有規(guī)律的改變很相似，因此我們分析的重點應(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

11、成比例，其中纖維混凝土試件中鋼纖維體積摻率均為10。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是一個纖維端鉤被拉直，纖維端部周圍混凝土被擠碎的過程。當(dāng)纖維端鉤最終被拉直時，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，上述過程歷時也更短。因此當(dāng)基體強(qiáng)度較高時，軸拉應(yīng)力應(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型纖維長徑比最小，基體強(qiáng)度較高時出現(xiàn)了纖維拔斷

12、現(xiàn)象，因此當(dāng)基體強(qiáng)度增加時韌性指數(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持續(xù)過程，因此基體強(qiáng)度升高對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(c30和c60)，f3型鋼纖維的增韌作用優(yōu)于f4型。當(dāng)基體強(qiáng)度很高時(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來超過了f3型鋼纖維。3.3鋼纖維鋼筋混凝土單軸拉伸應(yīng)力應(yīng)變曲線

13、典型的鋼纖維高強(qiáng)混凝土軸拉應(yīng)力一應(yīng)變?nèi)€(為了便于比較，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。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，鋼纖維摻量的提高可以大大地改善曲線的豐滿程度。鋼纖維類型對軸拉應(yīng)力一應(yīng)變?nèi)€的形狀也有一定的影響。fl型纖維的曲線是幾種鋼纖維中最豐滿的，并且在拉應(yīng)變?yōu)榇蠹s10000個微應(yīng)變時出現(xiàn)了第二峰值。該現(xiàn)象體現(xiàn)了fl型纖維良好的增韌效果。當(dāng)基體強(qiáng)度較高時，由于纖維拔斷的出現(xiàn)使得f2和f3型鋼纖維

14、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。這是因為長直形鋼纖維的拔出過程是相對連續(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)沒有達(dá)到使混凝土材料實現(xiàn)應(yīng)變強(qiáng)化的地步，大部分試驗曲線都在達(dá)到峰值后，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)，而另外兩條則沒有，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)力峰值點為分界點。本文中

15、，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： （4）這里： 和 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，dydx=e0 ep；3)x=1，y=1，dydx=0由邊界條件可得公式(5)可以簡化為：（5）系數(shù) 可以通過試驗數(shù)據(jù)回歸獲得 (6)式中： e0為圓點切線模量；ep 為峰值應(yīng)力點割線模量(第一峰值)。因此公式(6)可以轉(zhuǎn)換為： (7)4.2下降段公式下降段數(shù)學(xué)的模型為： （8）式中：和 為與基體和鋼纖維特性有關(guān)的參數(shù)。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

16、最小二乘法回歸獲得：（9）可見基體強(qiáng)度和纖維參量對軸拉曲線下降段的下降速率的影響是相反的。五、 理論曲線與試驗結(jié)果的比較鋼纖維高強(qiáng)混凝土軸拉應(yīng)力一應(yīng)變理論曲線和試驗曲線的比較如圖l2所示(以試件f36010為例)?？梢姡碚摻Y(jié)果與試驗結(jié)果符合較好。六、實驗結(jié)論(1)試驗結(jié)果表明：鋼纖維高強(qiáng)混凝土劈拉強(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，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)度的比值基本不變；軸拉極限強(qiáng)度的比值有所變化，且該變化對不同的纖維類型有所不同，鋼纖維與基體黏結(jié)性能好，且破壞時不被拉斷

17、，則增強(qiáng)效果好。(3)提高鋼纖維摻量對鋼纖維高強(qiáng)混凝土的抗拉強(qiáng)度特性的改善作用比對普通強(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)來評價鋼纖維高強(qiáng)混凝土的韌性，鋼纖維混凝土的軸拉韌性要大大優(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)變曲線在峰值過后下降得越快；纖維摻量的提高可以大大改善曲線的豐滿程度，鋼纖維類型對曲線形狀也有一定的影響。通過對實驗曲線的分析與回歸，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。(

18、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fl型鋼纖維的增韌效果最好。外文翻譯原文concrete stress test1 test introductionthe tensile properties of concrete can be enhanced substantially by incorporating high strength and small diameter short steel fiberswhich leads to the steel fiber reinforced concrete(sfrc)in conventional sfrc，th

19、e steel fiber content is usually within the range of 022 by volumeat such a low 6her contentthe tensile response of sfrc would 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 postcrac

20、king response, represented by an increase in postcracking ductility due to the work associated with pullout of fibers bridging a failure crack. however，improvements in some other properties are insignificant moreover，the softening segment of the stressstrain curve of sfrc with such a low fiber conte

21、nt under uniaxial tension is difficult to be got with normal experimental methodsmany works have been done to find 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 ad

22、ded. in this article，the stressstrain behavior of sfrc under uniaxial tension was analyzed for different types of fiberthe tensile characteristics of sfrc influenced by the matrix strength and the steel fiber content were studied alsoin addition，the stressstrain curves of high strength sfrc with dif

23、ferent factors were well acquiredthe mechanism of fiber reinforced concrete to enhance research, to obtain 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

24、 must have enough stiffness to ensure the testing process stability. is well known in engineering practice, 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

25、 fraction are about 1%. in this paper the design of the axial tension sfrc material testing, fiber dosage to take 1%, and using different types of fiber-reinforced forms, were analyzed.2 experimental content the specimens were tested on a 60 kn universal testing machinefour high steel bars were adde

26、d to enhance the stiffness of the testing machinein addition，spherichinges were used to abate the initial axial eccentricity of the specimensit was ensured that specimens should be pulled under uniaxial tension by adjusting the four high strength bolts which connect the specimens to the crossbeamand

27、 the difference between the tensile strains of the opposite sides of the specimen should be less than 1 5 of their mean valuewhen the fiber content was low (0 and 0.5 by volume)，the cyclic quire the whole stressstrain.21 materials four types of steel fibers shown in table were chosen for this test t

28、hree of these fibers (f1，f2 and f3) were hookedend and the other one(f4)was smooth three concrete mixtures，shown in table 2，were investigatedwater reducing agents were used in c60 and c80 mixes(dk一5 made by dalian structure research institute and sika made in switzerland respectively). the compressi

29、ve strengths of these c30，c60，c80 mixes were determined according to “test methods used for steel fiber reinforced concrete”(cecs 13：89)8 3 at 28 days using 150 mm150 mm 150 mm cube saveraged results for 3 specimens are given in table 20rdinary portland cement(yielded by dalian huaneng onoda cement

30、company)of 325 and 525 (according to china standard) were chosenriver sand(modulus of fineness is 2.6)and crushed limestone coarse aggregates(520 bin) were usedtablematrixcodestrength gradeof cement(iso)cement kg/m3u/cratio sandratiosandkg/m3crushedstrnekg/m3waterreducingcompressivestrengthmpac3032.

31、54500.440.366671155-37.07c6052.55000.350.336021223dk-567.59c8052.56000.290.315351190sika82.9622 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 specim

32、ens are shown in table 323 items at the age of 28 daysplain concrete and steel fiber concrete specimens were tested for tensile strength，respectively .the tensile stressstrain curves were acquiredmany other tensile characters of the high strength steel fiber concrete such as tensile work，etc were ca

33、lculated also. enhanced class steel fiber reinforced 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) showed the fracture energy integral: to

34、ughening class steel fiber reinforced concrete 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 corresponds to the limit of tensile strain value and plain concrete rather, in the 100 around, indicat

35、ing a low rate of fiber-containing incorporation in improving the role of ultimate tensile strain of concrete is not very obvious. the toughening class sfrc second peak corresponds to a much greater strain, up to 1000, from this second peak has greatly enhanced the appearance of toughness. dramix fi

36、ber because of the length of other three 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 its peak level of 50%.

37、3 results and discussion31 crack stress and ultimate tensile strength the crack stress and ultimate tensile strength of different specimens are listed in table 3the addition of steel fibers into concrete increased its crack stress an d ultimate tensile strengthand the ratios of these two parameters

38、of sfrc to those of plain concreue (with the same mix proportion)are given in table 3，too311 effect of matrix strength an(1 fiber type from table 3it can be seen that the effects of steel fibers 0n crack stress are little influenced by the matsix strengththat is to saywhen the matrix strength increa

39、ses, the ratios of crack stresses of sfrc ( with the same type of fibers contained)to those of plain concrete ones with the same mix proportion are invariable however，the condition for ultimate tensile strength is differentwhen the matrix strength increasesthese ratios of ultimate tensile strengths(

40、shown in table 3)vary dissimilarly according to the type of steel fibermoreoverthe increments are bigger than those of crack stress the heightening efficiency of fiber f1 for ultimate tensile strength rises as matrix strength increasesit is because that the strength of this kind of fiber is very hig

41、h(1 100 mpa)no fiber broken was observed during the test and the hookedends 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 stressthe strengths

42、of fibers f2 and f3 are midhigh(700 mpa)they all have hooked ends and both of their surfaces are coarsewhen the matrix strength was high(c80)fiber breaking occurred in the testand this phenomenon impaired the heightening efficiency of these two kinds of steel fiberso they should be used in middle st

43、rength concrete to exert their strengthening effect more efficientlyfiber f4 is smoothand its bond stress with matrix is comparatively lowt1ereforeits strengthening effect is 1ess notable than those of other kinds of fiberbecause of the low bond stressno fiber broken was found during the test and it

44、s heightening efficiency for ultimate tensile strength rises as matrix strength increases312 effect of fiber content the effect of fiber content on the crack stress and u1ultimate tensile strength was investigated for sfrc contained fiber f3and the fiber content varied from 05 to 15 by volume(shown

45、in table 3)it can be seen from fig1 and fig2 that as the fiber content increases the crack stress and ultimate strength of sfrc improve obviouslymoreoverthe rising trends of the curves in these two figures are stupendously similarin other words，the effect of fiber content on the characters of tensil

46、e stress of sfrc is positive and consistenttable 4 fiber type factorsfiber code atf1 0.642f2 0.862f3 0.794f4 0.589 the tensile strength of sfrc can be calculated with the follow formula： (1)where，fft is the ultimate tensile strength of sfrc； the ultimate tensile strength of plain concrete with the s

47、ame mixing proportion；a，the fiber type factor，which is shown table 4； is the fiber content 0f volume and l/d is the aspect ratio of steel fibers.32 tensile strain and toughness characters321 crack strain and the strain at peak tensile load the tensile strains were acquired by averaging the readings

48、of the four displacement sensors fixed around the specimenin addition，the specimens whose difference between the tensile strains of its opposite sides is larger than 15 of their mean value were blanked out the crack strain or the strains at peak tensile load of sfrc are much bigger than those of pla

49、in concrete(as shown in table 5)and the increments go up as the matrix strength or the fiber content increasescompared to that on crack strainthe increscent effect of steel fiber onthe strain at peak tensile load is more remarkable322 tensile work and toughness modulus the tensile work was defined a

50、s the area under the load-displacement curve from 0 to 05 rainmoreover，a tensile toughness modulus was introduced(shown in table 5)it was defined as： (2) where，fft is the ultimate tensile strength of sfrc； a，the area of the cross section of specimenboth these two parameters were quoted to evaluate t

51、he toughness characters of sfrc under uniaxial tensionthe tensile toughness modulus is a dimensionless factorcompared to what the tensile work doesit can avoid the influence of the ultimate tensile strength when studying the toughness of sfrc it call be found from table 5 that the altering regularit

52、ies 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 modulus the relationship between the matrix strength and toughness modulus of sfrc with four kinds of steel fiber are shown in fig3whose fib

53、er contents are all 1oby volumetogether with that relationship of plain concretethe tensile toughness of sfrc is much better than that of plain concretethe tensile toughening effect of steel fiber is remarkableas the matrix strength risesthe brittleness of concrete increases obviously，and then the t

54、ensile toughness of plain concrete falls downthis phenomenon was also found on specimens containing fiber f1and f2the pulling out of fiber f1 from concrete is in fact a process of hook-ends being straightened and the matrixs being crushed around the hook-endwhen the hooked end is straightened at las

55、tthe tensile load falls down quicklythe higher the concrete strength. the larger the rigidity of the matrix and the shorter the time that the process mentioned above laststhusthe stress-strain curve falls down more quickly，and then the toughness modulus decreaseshowever，the toughening effect of fibe

56、r f1 is the best among these four kinds of steel fiberthe aspect ratio of fiber f2 is the least。and when the matrix strength is high， fiber breaking occurstherefore，the toughness modulus falls down continually as the matrix strength rises.the toughness modului of fibers f3 and f4 rise together with the matrix strengthboth the two kinds of fiber are snipped and their surfaces are coarsethereforethe friction is dominant in the proportions of bond stressbecause the friction between fiber and matrix increases along with the matrix strength，and the whole pulling out