| Ultra-high performance concrete(UHPC)has the advantages of ultra-high strength,high toughness,high durability and high volume stability unmatched by ordinary concrete,and has become a new type of special material with great development potential in the future.Coarse aggregate-containing ultra-high performance concrete(UHPC-CA)is mixed with gravel and other coarse aggregates in traditional UHPC,which not only reduces the self-shrinkage effect of concrete materials,but also reduces the engineering cost to a certain extent,and has great engineering application value.In this paper,several sets of beam tests and pull-out tests were carried out on the bond properties between ultra-high performance concrete containing coarse aggregate(UHPC-CA)and HRB500 high-strength steel bars,and the bond failure modes and failure mechanisms of each specimen were studied in depth,analyzed the influence of parameters such as steel fiber,steel bar,bond length on the bond performance,and based on the test results,gave the empirical formula of each bond anchoring characteristic value,and established the "four-fold line" bond-slip constitutive Suggested formulas for calculating relationships and anchorage lengths.The main research contents are as follows:(1)Through the bond performance test of 20 beam-bonded specimens and 9direct-drawn specimens,the bond failure morphology and failure mechanism of each group of specimens were deeply analyzed,and the bond-slip of each group of specimens was analyzed.The characteristics of the curve in each stress stage were compared,and the influence of different test methods on the bond-slip curve was compared;Influence law of mid-span deflection.(2)Based on the test results of the steel bar strain along the bond length,the distribution of bond stress along the bond section was calculated,and the effects of steel fiber content,water-binder ratio and bond length on the bond stress distribution along the bond section were analyzed.According to the influence law,the bonding position function that reflects the relative size of bonding stress at different positions is established.(3)Combined with the bond-slip curve,the bond and anchorage eigenvalues of each group of specimens are given,the main influencing factors of each anchorage eigenvalue are analyzed,and the empirical formulas for the anchorage strength eigenvalues and anchorage slip eigenvalues are put forward.The obtained bond-slip curve is simplified,and a "four-fold line" bond-slip constitutive relation model is established.The model has good practicability and representation.(4)The anchoring state and anchorage reliability of HRB500 high-strength steel bars in UHPC-CA are analyzed,and the suggested anchoring length value of HRB500 high-strength steel bars in UHPC-CA is given according to the center point method;The critical and ultimate anchorage length of HRB500 high-strength steel bar in UHPC-CA,the proposed calculation formula of anchorage length and the value range of correction factor are put forward. |
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