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%; while cracking from the basic to the crack width of 0.5mm 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 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 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 Discussion

    3．1 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 concrete (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 mat six 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 M Pa)．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 M Pa)．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．and its bond stress with matrix is comparatively 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． 混凝土应力英文文献和中文翻译(3):http://www.751com.cn/fanyi/lunwen_15707.html