【正文】 Ep；3)X=1，Y=1，dy／dx=0．由邊界條件可得公式(5)可以簡(jiǎn)化為：因此公式(6)可以轉(zhuǎn)換為：。系數(shù)的取值通過最小二乘法回歸獲得：（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。可見，理論結(jié)果與試驗(yàn)結(jié)果符合較好。(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)度的比值基本不變；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，則增強(qiáng)效果好。(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。(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(duì)曲線形狀也有一定的影響。(7)綜合而言，四種鋼纖維中，F(xiàn)3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。 while cracking from the basic to the crack width of interval (the corresponding strain of about 2000με) showed the fracture energy integral: toughening 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 100με around, indicating a low rate of fibercontaining 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 1000με, From this second peak has greatly enhanced the appearance of toughness. DRAMIX Fiber 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 10000με its peak level of 50%.3 Results and Discussion3．1 Crack stress and ultimate tensile strength The 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 same mix proportion)are given in Table 3，too．3．1．1 Effect of matrix strength an(1 fiber type From 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 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 different．When the matrix strength increases．these ratios of ultimate tensile strengths(shown in Table 3)vary dissimilarly according to the type of steel fiber．Moreover．the increments are bigger than those of crack stress． The heightening efficiency of fiber F1 for ultimate tensile strength rises as matrix strength increases．It is because that the strength of this kind of fiber is very high(1 100 MPa)．No fiber 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 F3 are mid—high(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 of these two kinds of steel fiber．So they should be used in middle strength concrete to exert their strengthening effect more efficiently．Fiber F4 is smooth．a(chǎn)nd its bond stress with matrix is paratively low．T}1erefore．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 and its heightening efficiency for ultimate tensile strength rises as matrix strength increases．3．1．2 Effect of fiber content The 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 1．5％ by volume(shown in Table 3)．It can be seen from Fig．1 and Fig．2 that as the fiber content increases． The crack stress and ultimate strength of SFRC improve obviously．Moreover．the rising trends of the curves in these two figures are stupendously similar．In other words，the effect of fiber content on the characters of tensile stress of SFRC is positive and consistent．Table 4 Fiber type factorsFiber code atF1 F2