Theoretical And Numerical Cyclic Bond-slip Model Of Reinforcement Under Lateral Complex Stresses

The key to ensure the cooperative work of reinforcement and concrete lies in the good bond between reinforcement and concrete.Under repeated loading,such as earthquakes,when the slip between reinforcement and concrete is in the inelastic stage,the damage of the bond property is a cumulative process,and this damage is irreversible.Therefore,the degradation of the bond stiffness of reinforced concrete will lead to greater slip between reinforcement and concrete.When the degradation of the bond stiffness occurs at the key parts of the structure,it will cause the stiffness degradation of the members,which will eventually lead to the decline of the seismic capacity and bearing capacity of the structure.So,it is very necessary to study the bond-slip hysteretic behavior of reinforced concrete under repeated loading.At present,there are two main problems in the study of the bond performance of reinforced concrete under the coupling of complex stress and repeated loading.On the one hand,most studies have considered the bond slip relationship under monotonic load.Under repeated loading,the concrete protective layer may begin to peel off and the steel reinforcement may deteriorate due to splitting.On the other hand,some studies of repeated loading do not consider cumulative slip,and only consider the influence of control displacement,number of cycles and the thickness of concrete protective layer in the damage factors.In practical engineering,the components will not bear the established control displacement and time.In order to solve the above problems,a bond-slip analysis model of reinforced concrete under the coupling of repeated loading and lateral complex stresses was proposed.And a corresponding numerical model was proposed based on the four-node plane bond element and ABAQUS subroutine.The rationality and feasibility of the cyclic bond-slip model of reinforced concrete under complex stresses are preliminarily verified by pullout test blocks.Finally,the theoretical model and numerical model are verified to have good prediction effects through the simulation of anchorage defective components.The specific work is as follows:(1)The bond-slip cyclic theoretical model of reinforced concrete under lateral complex stresses has been put forward.The envelope curve refers to the bond-slip empirical formula of reinforced concrete under complex stresses.According to the test data,the parameters in the hysteresis criterion are re-checked,considering the effect of cumulative displacement on the bond performance.cumulative slip and historical maximum slip are introduced to describe the degradation of the bond performance.(2)The bond-slip cyclic numerical model of reinforced concrete under complex stresses has been proposed.The planar four-node bondelement is introduced,and the UEL and URDFIL subroutines of ABAQUS are used to record the slip of each analysis step,calculate the cumulative slip,judge the maximum slip in history,and update the lateral stresses of concrete in real-time.(3)The proposed numerical model is applied to the numerical simulation of defective anchorage components.It is applied to the column and foundation joints under monotone load and the beam-column joints under repeated loading.The validity and accuracy of the bond-slip theoretical model and numerical model proposed in this paper are verified by analyzing the displacements-pullout reaction force,slip-bond stress and reinforcement stress distribution.At the same time,the calculation results can reflect the advantage of this numerical model is to consider the real-time changing complex stresses of concrete effect on the bond-slip properties.using the fixed lateral stresses calculate bond stress is the most case,but the interaction of reinforcement and concrete will make concrete lateral stresses change.Therefore,the method of using fixed lateral stresses to predict the bond performance is not reliable,and the results predicted by this numerical model can solve the above problems well.