| A kind of new high performance fiber reinforced concrete, Ultra High Toughness Cementitious Composites (abbreviated as UHTCC), which shows prominent toughness and superior durability has been successfully applied in many practical projects overseas. When the UHTCC members are reinforced by steel bar, except for the fundamental material mechanical properties of UHTCC and steel bar, bond behavior between them is one of the basic problems of structure design. Therefore, pull-out tests, beam tests and inner-embedded stain-gauge tests are performed in this paper, with emphasis on the bond behavior and bond-slip relationship between UHTCC and steel bar. Meanwhile, the bond anchorage reliability analysis is also carried out. The major contributions are summarized as follows:1. Through the analysis of the typical bond-slip curve obtained by the pull-out tests, the curve can be divided into five stages as follows: micro-slip stage, slip stage, pullout stage, decline stage and residual stage. The characteristic of each stage, the process of bond failure and failure mode are studied. Moreover, a comparison between the bond behavior of reinforcing bars embedded in UHTCC and ordinary concrete is drawn.2. Based on the results of the pullout tests, the influences of the thickness of UHTCC cover, anchorage length, bar diameter and the shape of bar's surface on anchorage behavior is studied. The results of experiment show that the ultimate bond strength enhances with the increase of cover thickness, but it does not change when c/d is more than 5. In addition, the ultimate bond strength decreases with the increase of anchorage length and bar diameter. The equation to analyze bond strength between steel bar and UHTCC is established through statistics and regression, and the results well agree with the test.3. Through the beam tests, the anchorage behavior under moment and shear is studied. It indicates that the failure mode of the beam specimen shows better ductility under moment and shear. Compare with the pull-out test, the ultimate bond strength of beam test is smaller than that of pull-out test.4. Pull-out tests of a total of six specimens are performed in this paper. Along anchorage length of steel bar, a series of inner-embedded strain gauges are arranged at different positions. Based on measured steel bar strain and slip displacement at the free end of steel bar, the distribution of the bond stress and relative slip-displacement along the anchorage length of reinforcement bar are calculated. Then, the varying bond-slip relationship along anchorage length and the position functions reflecting the variation are deduced. Finally, the bond-slip relationship considering anchorage position is constructed. Moreover, a detailed analysis of their differences is carried out, compared to the bond-slip relationship between concrete and steel bar.5. Based on the experimental studies, the suggested anchorage length of deformed steel bar is given by reliability analysis, which provides references for engineering design. The formula of the anchorage length in existing "Code for design of concrete structures" is revised so that it can apply to calculate the anchorage length between steel bar and UHTCC.
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