Study On Prestress Transfer Of Pretensioned Concrete Members Under Local Corrosion

Pre-tensioned concrete bridge is widely used in small/medium span bridge system,public transport facilities due to its superiority of convenient construction and simple production process.However,service bridge structure in the natural environment will be affected by the chloride ion erosion,cause strand corrosion damage,concrete cover cracking,and weakens the bond between strand-concrete interface,affects the prestress transfer between the prestressed strand and concrete interface,the service safety of bridge structures is further threatened.This paper focuses on investigating the prestress transfer behavior in pre-tensioned concrete members under local corrosion.The main research works are as follows:(1)Experimental study on prestress transfer behavior in pre-tensioned concrete members under local corrosion was carried out.To analyze the influence of corrosion position and corrosion loss on prestress transfer,ten pre-tensioned concrete beams were designed and manufactured,corroded prestressed concrete beams with different corrosion positions and corrosion degrees were obtained by electrochemical accelerated corrosion method.Experimental result indicates that,the greater the corrosion loss of strand and the closer the corrosion position to the end area,the greater influence of prestress transfer in pretensioned concrete member.(2)A method for evaluate the prestress transfer in pre-tensioned concrete members under strand corrosion is developed,based on piezoelectric signal analysis theory.By Analyzing the frequency domain signal and wavelet packet energy,the relationship between the time of releasing,the time of corrosion and the load value and the piezoelectric signal in the prestressed transfer area is revealed.Results indicates that,the signal of the stress transfer zone weakens obviously before and after the tension of strand,the piezoelectric signal is slightly enhanced at the initial stage of corrosion,and attenuates after the appearance of corrosion crack.This method can effectively evaluate the prestress transfer of strand at the stage of corrosion free expansion and concrete cracking.(3)A prediction model for the transfer length of prestressed concrete members under the coupling effects of "Hoyer effect" and strand corrosion is proposed.Considering the coupling effects of "Hoyer effect" and strand corrosion,the displacement coordination relationship between strand-concrete interface and the softening behavior of concrete are analyzed based on the thick-walled cylinder theory.The formulas for calculating the expansive pressure at the strand-concrete interface in prestressed concrete beams under strand corrosion are derived.And the validity of the proposed transfer length prediction model is verified by experimental data.The sensitivity analysis of the parameters affecting the transfer length of prestressed concrete beams is carried out by the proposed transfer length prediction model.Analysis result shows that the effect of Poisson’s ratio on the transfer length of strand is more obvious than the elastic modulus of concrete.