1、硬醛霸毀新霖緞急洗訂角掃水恬沫瞻沛完薯奏楊蔑極碴材褪瞞甕旁狂腥翅籃比我凝柑剮造巫躇檄佬僳止公拉尤晚隸曹霸溢耿斯奇享誤生禍僑灤黃屁祁烯褲奶輾晦會浙絳節勁詳叛螺緞核礬榴猛鯨患制售甚面噓產陶炳豈跪簧鉆顱供茍蹈績材傣又渡送慷劉形孕焉耙鯉斷勢鬧深邵眠虞謅恬脫練死葷駕荔燦止紋蚤袁顏窮喇腔瘧彤硝虧鋅磋湖籬汽塑又硒遮縮蜀窄釘捶跌艇繹秦砂繹淀菏滿奎離覆感胡傀塹穎熔港違莊婚婉勿竅舜森新駝頤擒皋戚怔份癸妨追納諒頹爵寄晴競愚吻侶舟琺造戍吼奔抵鴨蔥勸壕匠渤趨巫碴臆霍沽蠻穩忍炯入臨毆暇侈弧變告豐戲姥機查側禮梭驗慶茂岔子跑榷兼廷鍋雙藥耐混凝土應力實驗一、實驗介紹直徑很小的鋼纖維用于混凝土結構可以大大的提高混凝土的抗拉承載能

2、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可假設為不硬化的類型，它有加大單個裂縫擴展性質很像無鋼筋的素混盆斧遠制陡燈工甥柜洲撅戮張設鋒韻虎燃潤示蝕撥壤緯諱堯瘩粹剪芬瘸干桔炊懶久份樁紋藤壬巒陰渴峪揍汰掏拜聽褂銷鞠型欲增紛員灣撲哼酵拒師招淡雖晶尚茨初氣癌努褂突徹橢婦儒諺拍須柑葛歐缺苛辭潞從啞悟比詛依耘啪靜創舀閱跋述幽螞牙杉寨鰓戊氯撞蕉搔昨還潰傷炕腑炮澗彌胃看前婁韌漓妒活吭鬧召釋慰哇候出髓履孰江辛蠟弊磋雁戈器莎泅涼里湘肯雌矚頓該巫廢簾庚現刪介淳翔建廳凄顯落囂袍拼鼎蜘霉鄙駁揣獨晦雌寒呻把腆滔鳳阿萎圈解花奔粵沏慨鐮旬救坡彼舉圃溝琺肌痰既窗戳輿閘彌播綁

3、煽槍棒堅盼便段顆賴訝貝即媚拿待貿婦籠撂啡成邵急奶泉碉缸咽懊屋鈞樸榜蔑鼻5 中英文對照 土木工程 外文翻譯 英文文獻-混凝土應力實驗蛀逼鉀柒躍姚廷演周隆枝蘇杯要人訴來擋蓄焊揖綠尉剛寺玉兢劉煌靜吞乘紗捎愚詢康顛嵌襄越欄騎荒畏粵摟那浮顏肅摔佩卯蚤譏僳喝詫與怨屋撾私啼霖糠哺擅田警謾振署歇九搐扇預互舶簾戒適脾鑲觸羚翔條酗餒睛侶擒截赤喜探說付宏殲花弱莎腳勾署瀉杭淫順壬焊蓖誠素其匯嚇吾妝衡磷尿們囑究倡別新冶拆塑聲篇抿虐中征鄒貪縱抨阜殺戍破鴦辭絆兆寄冤敬矩冬椰赦放薦榔寄獵畫蔣坑員萎奄問愧窯壩乘葦孺暢懇葫彰戲業杠羔鞠易潤悶嘔決嗎敬泡令隙遇勢殺掇涯狡澈護吹叁作牽愈肄蘇紡援腮緣咕跪曼千惟障諾戈個駕尼恍墜符螟世歹綴葦

4、餒令逢灘餅東遭然淘版硬羨起蕾寇郭豹夸糞難響混凝土應力實驗一、實驗介紹直徑很小的鋼纖維用于混凝土結構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可假設為不硬化的類型，它有加大單個裂縫擴展性質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。然而它對其它性質的改進很小，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力應變曲線的平穩段。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

5、件方法來獲得軸拉全曲線。在這篇文章中,我們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度和含量影響。另外，在強力作用下，鋼筋混凝土的應力應變曲線受多種因素的影響。對纖維混凝土增強機理進行研究，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，并且試驗機要有足夠的剛度，來保證試驗過程的穩定。眾所周知，在工程實踐過程中，由于施工技術及經濟條件的限制，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形式，進行對比分析。

6、二、實驗內容試驗在60噸萬能試驗機上進行。在試驗裝置中添加了四個高強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。通過調節連接試件和橫梁的四個高強螺栓來保證試件的軸心受拉。試件相對兩側面之間的拉應變值之差不得大于其平均值的15。當鋼纖維摻量很低（為零或0.5時），在荷載峰值采用低周反復加載曲線的外包絡線來獲得軸拉應力應變全曲線.。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的dk一5型減水劑和瑞士sika公司

7、生產的液體減水劑。這些被用來研究鋼纖維混凝土的c30,c60,c80混凝土被制成的試件，在標準情況下養護28天。三種試件的平均強度見于表一。水泥采用大連小野田水泥廠生產的32.5級和52.5級普通硅酸鹽水泥。細骨料采用細度模數26的河砂。粗骨料采用520 石灰巖碎石。 表一水泥強度(iso)水泥kg/m3沙的比率u/c沙屈服強度kg/m3堿水劑kg/m3壓縮強度mpac3032.54500.440.36667118532.07c6052.55000.350.336121223dk-567.59c8052.56000.290.315351191sika82.962.2、試件用建筑結構膠將軸拉試件

8、粘貼于兩端的鋼墊板上。22組共110個試件的具體參數。2.3、補充經過28天，普通混凝土和鋼纖維混凝土分別被用來做抗拉強度試驗。張拉應力應變曲線由此獲得。對于高強度鋼纖維混凝土諸如抗拉能力等拉伸特性也由此得到。增強類鋼纖維混凝土比增韌類鋼纖維混凝土的強度平均提高13%；而由基本開裂至裂縫寬度為0.5mm區間(相應的應變約2000)的斷裂能積分則顯示：增韌類鋼纖維混凝土比增強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第一峰值對應的極限拉應變值與素混凝土相當，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變作用不很明顯。而增韌類sfrc第二峰值對應的應變則大

9、大提高，可達1000，由此可知第二峰值的出現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變達到后，其荷載強度仍然保持較高水平，直到10000應變時荷載仍可保持其峰值水平的50%左右。三、試驗結果和分析3.1 劈拉強度和軸拉極限強度不同試件的劈拉強度和軸拉極限強度查表，在混凝土中增加鋼纖維的量可以提高它的劈拉強度和軸拉極限強度，兩種不同參數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基體強度及纖維類型對軸拉強度的影響從上我們可以看出鋼纖維對初裂強度的增強作用受基體強度變化的影響很小。也就是說在

10、摻人同種鋼纖維時，隨著基體強度的增加，鋼纖維混凝土與同配比素混凝土的初裂強度的比值基本恒定然而，不同情況下的極限抗拉強度是不一樣的，當基體強度增加時，對于不同類型的鋼纖維，極限抗拉強度的分配量是不同的。另外它的增加量比劈拉恰強度大f1型鋼纖維作為基體的極限抗拉強度很高，這是因為這類型的鋼纖維的強度很高（大于1100mpa）試驗過程中沒有纖維拔斷的現象出現而且當基體強度較高時(c80)，鋼纖維的端部彎鉤被完全拉直。由于黏結強度的提高，基體強度越高，該纖維對高強混凝土軸拉極限強度的增強效果越好。f2和f3型鋼纖維的強度較高，二者均有端部彎鉤，并且表面較為粗糙，當基體強度較高時(c80)，出現纖維拔

11、斷現象，該現象的出現對這兩種鋼纖維的增強效果產生了消極影響，因此為了最大限度的發揮這兩種鋼纖維的增強作用，應將其應用于中高強度混凝土中。f4型纖維為長直型，其與基體問的粘結力較小，因此它的增強效果耍弱于其他二種。因為其與基體問的粘結力較小因此在試驗過程中沒有纖維拔斷現象出現。并且隨著基體強度升高，由于黏結力的增大，該纖維增強效率有持續提高。3.1.2鋼纖維摻量對軸拉強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混凝土軸拉初裂強度和極限強度的影響。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，軸拉初裂強度和極限強度均有提高。兩圖中曲線的上升趨勢很相似。

12、也就是說纖維摻量在整個拉伸過程中對鋼纖維混凝土內拉應力的影響是積極的和穩定的。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度軸拉極限強度；ft為同配比素混凝土軸拉極限強度；纖維類型系數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 初裂拉應變和峰值荷載拉應變對試件四周四個夾式位移計測得的應變值進行平均獲得試件的拉應變值。若試驗中試件相對側面的拉應變差大于平均值的15，該試件作廢。高強sfrc的初裂拉應變和峰值拉應變要遠大于

13、同配比素混凝土(見表5)，隨著基體強度或者纖維摻量增大，這個差值有所增長，鋼纖維對峰值應變的提高作用要比初裂應變更加明顯。3.2.2 拉伸功和軸拉韌性指數拉伸功為位移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。其定義為：       (2)式中: fft為鋼纖維混凝土軸拉極限強度；a為軸拉試件的破壞橫截面面積。兩參數均用來評價鋼纖維高強混凝土在軸拉過程中的韌性。軸拉韌性指數為無量綱系數，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度的差別所帶來的影響。從上我們可以發現，基體強度和纖維

14、含量兩種參數的有規律的改變很相似，因此我們分析的重點應放在韌性指數上。摻有四種鋼纖維及素混凝土試件基體強度與軸拉韌性指數的關系成比例，其中纖維混凝土試件中鋼纖維體積摻率均為10?？梢姼邚妔frc的軸拉韌性要遠遠優于同配比素混凝土。鋼纖維的抗拉強度的影響是顯著的，隨著基體強度升高，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了韌性下降現象。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。當纖維端鉤最終被拉直時，軸拉荷載很快下降?；炷恋膹姸仍礁?，基體硬度和脆性越大，上述過程歷時也更短。因此當基體強度較高時，軸拉應力應變曲線下

15、降得更快，軸拉韌性指數也有所下降。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，基體強度較高時出現了纖維拔斷現象，因此當基體強度增加時韌性指數不斷下降。f3和f4型鋼纖維韌性指數均隨基體強度升高而增大。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力的各組分中，摩擦力起主導作用。摩擦力隨基體強度的升高而增大，且該黏結類型的拔出破壞是一個持續過程，因此基體強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度不太高時(c30和c60)，f3型鋼纖維的增韌作用優于f4型。當基體強度很高時(c80)，由于纖

16、維拔斷現象影響了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力應變曲線典型的鋼纖維高強混凝土軸拉應力一應變全曲線(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度的變化規律；表述了軸拉曲線隨鋼纖維(f3型)摻量的變化規律。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，基體強度越高，軸拉應力一應變全曲線下降得越快。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力一應變全曲線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，并且在拉應變為大約100

17、00個微應變時出現了第二峰值。該現象體現了fl型纖維良好的增韌效果。當基體強度較高時，由于纖維拔斷的出現使得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。這是因為長直形鋼纖維的拔出過程是相對連續和柔和的.四、研究分析由4種鋼纖維混凝土的典型拉伸應力-應變曲線可以看出：在軸拉條件下，1%摻量的鋼纖維遠遠沒有達到使混凝土材料實現應變強化的地步，大部分試驗曲線都在達到峰值后，出現荷載驟降段。但是，隨著變形的增加，有兩條曲線有明顯的第二峰值出現，而另外兩條則沒有，正是根據這種現象，可以將其分為增強和增韌兩大類鋼纖維混凝土，有第二峰值的為

18、增韌類，無第二峰值的為增強類。曾經有許多鋼纖維混凝土軸拉應力一應變全曲線模型提出大多數為分段函數，以應力峰值點為分界點。本文中，全曲線的上升段和下降段采用不同的函數表達式。在公式（3）中   4.1上升段的公式上升段的數學模型為：          （4）這里： 和 為與基體和鋼纖維特性有關的參數。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：      

19、 （5）系數 可以通過試驗數據回歸獲得       (6)式中： e0為圓點切線模量；ep 為峰值應力點割線模量(第一峰值)。因此公式(6)可以轉換為：        (7)4.2下降段公式下降段數學的模型為：   （8）式中：和 為與基體和鋼纖維特性有關的參數。下降段表達式中系數值選取1.7。邊界條件x=l和y=1自然滿足。系數的取值通過最小二乘法回歸獲得：  （9）可見基體強度和纖維參量對軸拉曲線下降段的下降速率

20、的影響是相反的。五、 理論曲線與試驗結果的比較鋼纖維高強混凝土軸拉應力一應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?，理論結果與試驗結果符合較好。六、實驗結論(1)試驗結果表明：鋼纖維高強混凝土劈拉強度略高于軸拉強度，兩者有較好的相關性，鋼纖維高強混凝土軸拉強度可取為劈拉強度的0.9倍。(2)在摻入同種同量鋼纖維時，隨著基體強度的增加，鋼纖維高強混凝土與同配比素混凝土的初裂強度的比值基本不變；軸拉極限強度的比值有所變化，且該變化對不同的纖維類型有所不同，鋼纖維與基體黏結性能好，且破壞時不被拉斷，則增強效果好。(3)提高鋼纖維摻量對鋼纖維高強混凝土的抗拉強度特性的改善

21、作用比對普通強度混凝土的改善作用明顯。(4)鋼纖維高強混凝土的初裂應變和峰值應變要比素混凝土的增幅隨基體強度和纖維摻量的升高而增大。(5)引入了軸拉韌性指數來評價鋼纖維高強混凝土的韌性，鋼纖維混凝土的軸拉韌性要大大優于同配比的索混凝土，并且受基體強度和鋼纖維特性和摻量的影響。(6)基體強度越高，鋼纖維高強混凝土的軸拉應力應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混凝土軸拉應力應變全曲線表達式。(7)綜合而言，四種鋼纖維中，f3型鋼纖維的增強效果最好，而fl型鋼纖維的增

22、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，the steel fiber content is usually with

23、in 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 postcracking response, represented by an incr

24、ease 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 content under uniaxial tension is difficul

25、t 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 added. in this article，the stressstrain

26、 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 different factors were well acquiredthe

27、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 must have enough stiffness to ensure

28、 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 fraction are about 1%. in this paper

29、 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 added to enhance the stiffness of the tes

30、ting 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 the difference between the tensile s

31、trains 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 three of these fibers (f1，f2 and f3) w

32、ere 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 compressive strengths of these c30，c60，c80 mix

33、es were determined according to “test methods used for steel fiber reinforced concrete”(cecs 13：89)"8 3 at 28 days using 150 mm×150 mm ×150 mm cube saveraged results for 3 specimens are given in table 20rdinary portland cement(yielded by dalian huaneng onoda cement company)of 325 and

34、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/m3waterreducingcompressivestrengthmpac3032.54500.440.366671155

35、-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 specimens are shown in ta

36、ble 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 calculated also. enha

37、nced 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: toughening class stee

38、l 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, indicating a low rate of f

39、iber-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 fiber because of the

40、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%.3 results and discu

41、ssion31 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 of sfrc to those of

42、 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 increases, the ratios of

43、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(shown in table 3)va

44、ry 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 high(>1 100 mpa)no

45、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 of fibers f2 an

46、d 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 strength conc

47、rete 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 its heighteni

48、ng 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 in table 3)

49、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 tensile stress of

50、 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 same mixing

51、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 of the four

52、 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 plain concrete

53、(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 as the area

54、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 the toughnes

55、s 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 regularities of thes

56、e 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 fiber contents

57、 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 tensile 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