Bond Behavior Of Weakly Bonded Ultrahigh-strength Steel Bars Embedded In Medium-high Strength Concrete

Based on the concept of seismic damage-controlled design,the reasonable application of weakly-bonded ultrahigh-strength steel bars and medium-high strength concrete to design post-earthquake resilient structures is the demand for developing energy-saving and environment-friendly resilient cities.In order to provide scientific basis for engineering design and seismic damage reduction analysis,this thesis reveals the bond behavior of weakly-bonded ultrahigh-strength reinforcing bars and mediumhigh strength concrete and medium-high strength recycled concrete based on experiments,and the main research contents and results are as follows:1.A monotonic loading test was completed on twenty-seven specimens between weakly bonded ultrahigh-strength reinforcement and medium-high-strength reinforced concrete,and the bond response of weakly-bonded ultrahigh-strength steel bars under different concrete strengths and anchorage lengths was analyzed to reveal the bond damage mechanism.By comparing the calculation results with the test results,the reasonableness of the analytical model was verified,and a bond stress-slip relation between weakly bonded ultra-high-strength steel bars and medium-high-strength reinforced concrete was established.2.A monotonic loading test was completed on fifty-one specimens between weakly bonded ultrahigh-strength reinforcement and medium-high-strength recycled concrete,and the variables included recycled concrete strength;recycled coarse aggregate replacement ratio;embedment length;concrete cover;antirust coating;volume fraction of steel fibers and stirrup ratio.By comparing the calculation results with the test results,the reasonableness of the predicted model was verified,and a bond stress-slip relation between weakly bonded ultra-high-strength steel bars and mediumhigh-strength recycled concrete was established.3.Nine monotonic loading tests on mechanical anchorage bond behavior of weakly bonded ultra-high strength reinforcement with medium-high-strength recycled concrete were completed,and the effects of different mechanical anchorage methods on the bond response between weakly bonded ultra-high strength steel bars and medium-high-strength recycled concrete were analyzed.The recommendations for the design of weakly bonded ultra-high strength reinforcement anchorage structures for medium-high-strength recycled concrete members were put forward.Main conclusions:(1)Concrete strength,recycled coarse aggregate replacement ratio,reinforcement anchorage length,concrete cover,steel fiber admixture,antirust coating,stirrup ratio,and mechanical anchorage method are the key parameters affecting the bond behavior of weakly bonded ultra-high-strength steel bars and medium-high-strength concrete.The bond strength between weakly bonded ultra-high-strength steel bars and mediumhigh-strength reinforced concrete increases with the increase of concrete strength,but decreases with the increase of anchorage length of reinforcement.(2)The failure mode of the medium-high-strength reinforced concrete and steel fiber reinforced concrete is weekly-bond reinforcement pullout,and the bond strength increases with the increase of stirrup ratio but decreases with the increase of steel fiber admixture.(3)The failure mode of the plain concrete specimens is concrete splitting damage,and the average bond strength with fully recycled concrete aggregate is 16.22% and7.22% higher than that of concrete with 0% and 50% recycled coarse aggregate replacement ratios,respectively.The bond strength increases with the increase of the concrete cover thickness.It can be seen that the bond strength of steel bars decreases by 30.53% with antirust coating on the surface.(4)The calculated values of the proposed bond strength analysis model and the predicted bond-slip relation are in good agreement with the experimental results,which can be used as a reference for computational analysis and engineering design.(5)Based on the experimental results,it is recommended to use bolt anchor head mechanical anchorage at the end of the reinforcement in actual projects to reduce the basic anchorage length of weakly bonded ultra-high-strength reinforcement and to ensure its reliable anchorage performance in concrete.