| Reinforced bar and concrete form the skeleton of engineering buildings,and the bonding betw een reinforce bar and concrete is the premise of working together.The fiber material with good tensile strength can effectively improve the tensile strength of the concrete.There have been many research results focused on the bonding of steel fiber reinforced concrete and steel bars,but there is still a lack of research on high-flow and high strength steel fiber reinforced concrete and high-strength steel bars.The new material changes the original bonding mechanism,and the influencing factors are complex,requiring systematic analysis through a large number of tests.In this paper,the research on the bonding properties of high strength steel bars and SRFC is carried out,and suggestions for design theory research and engineering application are given.The main research work is as follows:Through the central pull-out tests of 104 bonded specimen,the matching relationship between the SFRC of C40 and C50 and the steel bars of different steel bar diameters and strength grades was developed.The effects of concrete strength grade,steel fiber volume fraction,steel bar diameter and steel grade on the bond performance and free end slip are studied,and the bond slip constitutive relationship of SFRC and high strength steel bar is more suitable.The main findings are as follows:(1)The addition of steel fiber is advantageous for the improvement of the bonding property.When the steel fiber content is 0.8%and 1.2%,the bond slip strength increases between 10%and 20%when the C50 strength grade is matched with different steel bars.When the steel fiber content is greater than 1.6%,the increase is 20%?30%;the increase in internal splitting strength is increased by 40%?60%.Tests have shown that the incorporation of steel fibers is beneficial to enhance the chemical bonding strength.(2)The relative contact area between steel and concrete is the key to affect the bond strength.When the bonding section is the same as the anchoring length,the change of the diameter of the steel bar has little effect on the bonding strength,and the large-diameter steel bar is not conducive to improving the bonding performance.The amount of free end slip is proportional to the diameter of the bar.As the diameter increases,the descent segment of the bond slip curve is more gradual.(3)When the steel fiber content is 1.6%?2.0%,the bonding performance is good,and the influence of the steel strength grade and diameter is small.When the concrete strength grade is C50 and HRB500 steel bar is matched,the ultimate bond strength is increased by 10%?30%,and it is increased by 15?40%when matching with HRB400 steel bar.It is recommended that the base strength grade is C50,and the SFRC with steel fiber content of 1.6%?2.0%matches the HRB400 grade steel bar.When using HRB500 grade steel bars,it is recommended to increase the concrete grade to C60,which is beneficial to the full advantage of material performance advantages.(4)When the concrete strength grade is increased from C40 to C50,the diameter 14mm is greatly affected by the concrete strength grade,the ultimate bond strength is increased by about 30%,and the diameter of 20mm is increased by about 8%.Small-diameter steel bars match concrete with higher strength grades,which is beneficial to the improvement of bonding performance.The greater the concrete strength grade,the greater the residual bond stress and the more "full" curve.(5)The steel fiber influence factor k is introduced,and the falling section of the formula is modified to make the bond-slip constitutive relationship between SFRC and high-strength steel bar conform to the actual situation. |
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