Behavior Of Corrosion Fatigue Damage Of Steel Strand In Post-tensioning Prestressed Concrete Structures Under Chloride Environment

A large number of prestressed concrete structures are served in the chloride environment, and some of which withstand the typical fatigue load. The combined action of chloride corrosion and fatigue load can lead to the corrosion fatigue damage and failure of the steel bar, and then lead to the degradation of the structure and even the failure of the structure. In the past, experimental simulations about the combined effects of corrosion and fatigue were insufficient, so there is no scientific understanding which is closed to practical problems. In this paper, taking the steel strands which in the post tensioning prestressed concrete structures as the study object. Through the relatively long term test simulation which considered the interaction of corrosion and fatigue, this paper studies the coupling damage effect caused by them, and discusses the prediction method of full life working state of prestressed concrete structure under corrosion fatigue condition.By measuring the corrosion current density of steel strands which in the prestressed concrete structures under the coupling effects of corrosion and fatigue, this paper studies the influences of corrosion rate of steel strands caused by chloride ion concentration, fatigue stress amplitude, and fatigue time. The results shows that the corrosion rate increases with the increase of chloride ion concentration, fatigue stress amplitude, fatigue time, and the influence trend is approximately exponential function relation. Referring to the basic theoretical model and combined with the test results, the paper fitts the empirical model of the corrosion rate of steel strandds under fatigue coupling.The statistical analysis is carried out on corrosion pit features of steel strands which in the prestressed concrete structure under the fatigue coupling, and it also calculates pits volume and the stress-increasing coefficient, by which this paper studies the effects of fatigue and chloride content on the development of corrosion pits. By the research to provide reference for the corrosion fatigue coupling damage behavior of prestressed concrete structures. The results shows that the steel strands shows the typical characteristic of the pit corrosion, and all the pits in geometry are closed to saddle or ellipsoidal; pits depth, width, length, volume, stress-increasing coefficient and other parameters could better obey normal distribution and logarithmic normal distribution; with the increase of fatigue stress amplitude, the stress-increasing coefficient based on log normal distribution pattern of the 95 percentile value also increases.Through fatigue damage acoustic emission monitoring of the long-term corrosion fatigue test of steel strands, the research is carried out on the relationship between the steel strand damage process and the AE parameters. The results shows that the fatigue cumulative damage of steel strands is increasing with the increase of chloride ion concentration, fatigue stress amplitude and fatigue time.Based on the macroscopic observation and analysis on fatigue fracture surface’ morphology, color, roughness and crack propagation of steel strands, the paper deduces fracture process and analyzes the reasons of fracture.The paper discusses the durability and life prediction of concrete structures under chloride environment. According to the literature chloride ion diffusion model and combined with the empirical model of the corrosion rate of steel strands under the coupling of the corrosion and fatigue which obtains in Chapter 2, the paper obtains the life prediction model of prestressed concrete structures under the corrosion fatigue coupling and the durability design method of prestressed concrete structures.