【正文】 535 1190 Sika 2． 2 Specimen The tensile specimen was bonded to steel padding plates at both ends by tygoweld． A total of 1 1 0 specimens were divided into 22 groups according to certain parameters． The parameters of these specimens are shown in Table 3． 2． 3 Items At the age of 28 days． 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 reinforced concrete toughness category than the strength of steel fiber reinforced concrete an average of 13%。 六、實(shí)驗(yàn)結(jié)論 (1)試驗(yàn) 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 倍。 在公式（ 3）中 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)。 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s 10000個(gè)微應(yīng)變時(shí)出現(xiàn)了第二峰值。由于端鉤的存在使得在基體強(qiáng)度不太高時(shí) (C30 和 C60)， F3 型鋼纖維的增韌作用優(yōu)于 F4 型。混凝土的強(qiáng)度越高，基體硬度和脆性越大，上述過程歷時(shí)也更短。軸拉韌性指數(shù)為無量綱系數(shù)，與軸拉功相比，在評價(jià)軸拉韌性時(shí)可在一定程度上消除軸拉極限強(qiáng)度的差別所帶來的影響。 纖維序號 F1 F2 F3 F4 鋼纖維鋼筋混凝土軸拉極限強(qiáng)度可以用下式來計(jì)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。 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。而增韌類 SFRC 第二峰值對應(yīng)的 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 Mpa C30 450 667 1185 — C60 500 612 1223 DK5 C80 600 535 1191 Sika 應(yīng)變則大大提高，可達(dá) 1000με，由此可知第二峰值的出現(xiàn)大大提高了材料的韌性。細(xì)骨料采用細(xì)度模數(shù) 2． 6的河砂。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％。鋼筋混凝土的抗拉特型首鋼纖維的強(qiáng)度和含量影響。在一般情況下混凝土中摻鋼纖維的體積比例在 ％～ ％之間。眾所周知，在工程實(shí)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(shí)例中，纖維摻量都在 1%左右。 試驗(yàn)中所采用的三種混凝土配合比用于研究，見于表一。 22 組共 110 個(gè)試件的具 體參數(shù)。 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。 鋼纖維摻量對軸拉強(qiáng)度的影響 試驗(yàn)中重點(diǎn)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。 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，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?？梢姼邚?qiáng) SFRC 的軸拉韌性要遠(yuǎn)遠(yuǎn)優(yōu)于同配比素混凝土。 F3和 F4 型鋼纖維韌性指數(shù)均隨基體強(qiáng)度升高而增大。曲線由彈性階段、彈塑性階段和下降段 (軟化段 )組成。 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。 下降段表達(dá)式中系數(shù)值選取 。 (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。. Formula(4)can be simplified as： (5) And the value of can be calculated from experimental data as ： (6) where， Eo is the origin tan gent modulus； E p， secant modulus at peak load(the first peak) Thus， Formula(5)Call be inverted as： (7) 4． 2 Formula of falling section The digital model for the falling section is： (8) where， are parameters related to the characters of matrix an d steel fibers ． The value of is chosen as in the formula of falling section 10． the boundary condition X= 1， y= 1 is satisfied inherently． In addition． the value of a could be regressed with the method of least squares as： (9) it can be seen from the expression that the effects of the matrix strength and fiber content on the curve’s falling rate are opposite． 5. Comparison of Predictions and Experimental Results The parison of predictions and experimental results for stress—strain curves are shown in Fig． 1 2 (take the curves of F3—6010 as an example)． The theoretical curve and the experimental ones fit wel1． 6. Conclusions a)When the matrix strength increases， the ratios of crack stresses of SFRC (with the same type of fiber)to those of plain concrete ones with the saii3e mix proportion are invariable． These ratios of ultimate tensile strengths vary dissimilarly according to the type of steel fiber． Moreover， the increments ale bigger than those of crack stress and are influenced by fiber type． b)As the fiber content increases． the crack stress and ultimate tensile strength of SFRC improve obviously and the effect of the fiber content on the characters of tensile strength of SFRC is positive an d consistent． c)The crack strain or the strains at peak tensile load 0f SFRC are much bigger than these of plain concrete． In addition， the increments go up as the matrix strength or the fiber content increases． d)A tensile toughness modulus was introduced to evaluate the toughness characters of SFRC under uniaxial tension． The tensile toughness of SFRC is much better than that of plain concrete． In addition． it is influenced by the matrix strength and characters of steel fiber． e)The matrix strength is higher ， the stress—strain curves fall down faster． Otherwise， the rising of the fiber content can much improve the chubbiness of these curves． Moreover． the type of steel fiber has some effect on the shape of the stress—strain curve． f)The formula of the tensile stress—strain curve of SFRC was regressed． The theoretical curve and the experimental ones fit wel1． T}1is model may be helpful in the further research of SFRC under uniaxial tension．