Study On Retraction Slip Of Prestressing Strand In Pretensioned Concrete Members Under Local Corrosion

As the significant hub of transportation infrastructure system,the prestressing concrete bridge plays an important role in promoting national economic development,cultural exchange and resource allocation.However,the service environment of prestressing concrete bridge structure is extremely complex.The corrosion of prestressing strand is extremely easy to occur in the service environment which includes high temperature,high humidity and chloride salt.Corrosion leads to concrete cracking and bond degradation,which seriously threatens the durability and safety of the bridge structure.Therefore,a local corrosion experiment of prestressing strand is conducted to analyze the degradation of bond performance of prestressing strand and structural bearing capacity in this paper.The corresponding theoretical model and numerical model are established to study the retraction slip of corroded prestressing strand.The details include the following aspects:(1)An experimental study is conducted on ten pre-tensioned concrete beams to investigate the effect of local corrosion on the retraction slip of prestressing strand.The local corrosion specimens are obtained by electrochemical corrosion method.In the corrosion process,the retraction slip of prestressing strand and transfer length of specimens are analyzed.Then,a static loading test is carried out on the corroded specimens to explore the influence of local corrosion on the bearing capacity and stiffness of pre-tensioned concrete members.The results show that the retraction slip of prestressing strand and the transfer length of specimens increase with the increase of local corrosion loss.With the local corrosion position moving from the beam end to the middle span,the influence of the retraction slip of prestressing strand and the transfer length on the local corrosion is obviously weakened.For the bearing capacity and stiffness of specimens,when the local corrosion position gradually moves from the beam end to the middle span,both of them show performance degradation.(2)A theoretical model is proposed to predict the corrosion-induced retraction slip of corroded prestressing strand in pre-tensioned concrete members.Based on the thick-walled cylinder theory and considering the coupling effect of strand corrosion and Hoyer effect in the present theoretical model.The retraction slip of prestressing strand is deduced through the stress-strain coordination relation.The retraction slip of corroded prestressing strand under different parameters are discussed to evaluate the sensitivity of parameters.The prediction results were verified by the experimental results.The results show that the average error between the experimental values and the predicted values is 8.4%,which indicates that the proposed model can accurately predict the retraction slip of prestressing strand in the pretensioned concrete members under local corrosion.The retraction slip of prestressing strand is positively correlated with the diameter of strand,but negatively correlated with the compressive strength of concrete.Compared with the compressive strength of concrete,the diameter of strand has a more significant influence on the retraction slip of corroded prestressing strand.(3)A numerical model is established to simulate the retraction slip of corroded prestressing strand in pre-tensioned concrete members under local corrosion.Prestressing strand and concrete are modeled by solid elements,and cohesive contact behavior is utilized to simulate the bond-slip behavior between prestressing strand and concrete.This model is expected to simulate the whole process of applying prestress through pretension technique.The accuracy of the established numerical model is validated by contrasting the experimental,theoretical prediction and numerical simulation results.The results show that the cohesive contact model can effectively simulate the retraction slip behavior of prestressing strands under local corrosion.