Study On Dynamic Bond Performance Of Reinforcements In Concrete Under Lateral Tensile And Tensile-Compressive Stresses

The bond between reinforcements and concrete is the basis of their cooperative work,which directly affects the bearing capacity and deformation characteristics of reinforced concrete structures.In the numerical calculation for reinforced concrete structures,the reliability of the bond-slip constitutive model between reinfrocements and concrete also affects the accuracy of the numerical calculation.Under the action of external loads,the concrete surrounding the reinforcement may be under complex stress states,which may affect the bond performance between reinforcements and concrete.Especially when it is under the lateral tensile or tensile-compressive stresses,the bond performance between reinforcements and concrete will deteriorate.Meanwhile,since reinforced concrete structures will be subjected to dynamic loads,such as earthquakes,impacts,explosions,etc.,the dynamic bond performance between reinforcements and concrete also needs to be fully considered.At present,some achievements have been gained in the research on the dynamic bond performance between reinforcements and concrete.However,for the common existed complex stress states,the corresponding research on dynamic bond performance is still not comprehensive,only including that under lateral compressive stresses.Therefore,for the range of loading rate that structures will withstand under earthquakes,this thesis experimentally studies the dynamic bond performance between reinforcements and concrete under lateral tensile and tensile-compressive stresses with central pull-out specimens.The main contents and conclusions are as follows:（1）The dynamic bond performance of plain bars in concrete under uniaxial and biaxial lateral tensile stresses is studied,and the effect of loading rate on the bond performance under different tensile stress levels is analysed.The results show that as the lateral tensile stress increases,the bond strength decreases linearly while the slip at the peak bond stress s_uincreases linearly.Under different lateral tensile stress levels,the bond strength is independent of the loading rate,whereas s_u decreases with increasing the loading rate,which shows a linear relationship with the logarithm of the ratio of the loading rate,log（v/v₀）;（2）The dynamic bond performance of plain bars in concrete under tensile-compressive stresses is studied.The results show that under the same lateral compressive stress,as the lateral tensile stress increases,the bond strength decreases and s_u increases.The bond strength increases with the increase of the loading rate,which shows a linear relationship with log（v/v₀）,and the increasing rate of the bond strength is independent of the lateral tensile stress level but related to the lateral compressive stress level.The greater the lateral compressive stress,the larger the increasing rate.Meanwhile,the greater the loading rate,the smaller s_u;（3）The dynamic bond performance of deformed bars in concrete under uniaxial lateral tensile stresses is studied.The results show that the bond failure mode is independent of the loading rate and determined by the concrete strength,the concrete cover depth,and the level of lateral tensile stress.Based on the experimental results,the criterion for determining the bond failure mode is given.As the lateral tensile stress increases,the bond strength is weakened;as the loading rate increases,the bond strength is improved,and the effects of the lateral tensile stress and the loading rate on the bond strength when the splitting failure occurs are greater than those when the pull-out failure occurs.When the pull-out failure occurs,s_u is independent of the lateral tensile stress and the loading rate.When the splitting occurs,s_u is still insensitive to the loading rate,but it decreases significantly with increasing the lateral tensile stress;（4）Based on the variation of the bond parameters obtained from the experimental campaign,the calculation models for the dynamic bond parameters between reinforcements and concrete under lateral tensile and tensile-compressive stresses are established.According to these models,the bond strength and s_u under different concrete strengths,concrete cover thicknesses,lateral stress levels and loading rates can be calculated.The calculation accuracy of these models is verified by comparing with the experimental results.On this basis,a three-parameter bond-slip constitutive model is proposed,which is able to reasonablely describe the dynamic bond performance between reinforcements and concrete under lateral tensile and tensile-compressive stresses.