| After the column has been failed because of high strain rate load such as car bomb and explosion,the structure would collapse if the damaged span beam above the failed column couldn’t digest the upper load.Due to the characteristic extensional strain hardening and multiple cracking,Engineered Cementilious Composites(ECC)has the advantages of high ductility,high toughness,and small crack width,which makes ECC could replace the concrete in the damaged beam to provide resistance to the structure during the large deformation stage.The degree of bond slip between the rebar and ECC in the large deformation stage directly affects the resistance of the structure at the catenary stage.In addition,the structural column fails instantaneously,which produces obvious dynamic effects.Owing to inherent strain-rate sensitivity,the mechanical properties,deformation ability and constitutive relation of both rebar and ECC materials are all affected by the strain rate.Whereas,the bond-slip mechanism between ECC and steel bar is not clear and the constitutive relationship is not established under the high strain rate load,which makes hardly simulate the dynamic process of continuous collapse of the Rebar-ECC structure based on finite element software,This paper mainly carries out the following research:(1)Based on the characteristics of SHPB(Split Hopkinson Pressure Bar)device and bond slip test,the auxiliary device of SHPB for bond-slip test under high strain rates was designed to solve the problems of steel bar slip travel,non-planar contact between specimen and SHPB and lead-out of leading wire of strain gauge inside steel bar.(2)Totaled 108 impact specimens subjected to high strain rates load were designed by taking into account a few of factors such as strength grade of ECC,diameter of rebar and impact velocity.Three failure modes such as ECC split-reinforcement pull out,ECC split-reinforcement buckling and ECC split-reinforcement were found after the dynamic bond-slip test was fulfilled by SHPB.The failure patterns of dynamic specimens were reserved.Then Nine static specimens for comparing with dynamic bond-slip test were designed.The failure mode of ECC splittin-reinforcement pulling out wsa found after center drawing test.(3)Based on SHPB dynamic bond-slip test,the dynamically bond-slip curve(stress and slip curve)was measured,the bonding mechanism was revealed,the influence of various parameters for dynamic bond-slip performance was evaluated by three indexes including average ultimate bond-stress,average amount of slip and ultimate bond-rigidity.After the static center drawing test,the static bond-slip curve was measured and the influence of the diameter of reinforcement on the static ultimate bond strength was analyzed.The bond-slip curve was been taken a contrast between the dynamic bond-slip test data and the static bond-slip experimental data.The dynamic increase factor(DIF)was calculated by using the results of the static bond-slip test data as the reference value.(4)The distribution law of bond stress and relative slip between the Rebar-ECC within the anchorage length was deduced and analyzed by the data measured by strain gauge fitted inside the rebar.On the base of above analysis,a position function(ψ)(x)reflecting the distribution law of bond stress-slip relationship within the anchorage length was determined.A Bond-slip constitutive relationship(φ(s))includes two curves was proposed after the dynamic bond-slip test results compared with several existing bond-slip constitutive relationships.The average bond-slip constitutive relationship(τ(s,x))of Rebar-ECC under high strain rate considering the influence of anchorage position was established by position function and average bond-slip constitutive relationship. |
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