Study On Mechanical Performance Of Partial Prestressed Concrete Beams With Corroded Strand

The vehicle overloading and the environment corrosion are two major reasons for the fatigue life reduction of bridge structures. The vehicle overloading is liable to cause the fatigue damages of interior concrete, while the environment corrosion degrades structure durability and further increases the damage degree of interior concrete. In this thesis, the mechanical properties of corroded strands as well as the mechanical behaviors of partial prestressed concrete beams after strand corroded were investigated under monotonic static loading and constant-amplitude fatigue loadings. This study is an important part of the project of High Technology Plan of the National Department of Technology "Design Method of Concrete Beam Structure Based on Fatigue and Life"(Grant No.2007AA11Z133). The contents include four chapters in the paper as follows.1. Monaxial tension tests and fatigue tests were carried on a batch of corroded strands. The static and fatigue properties were studied. The monaxial tension test results showed that the plastic deformation ability, ultimate strength as well as elastic modulus of strands significantly decreased with the increase of corrosion rate. The fatigue test results showed that the fatigue life of strands decreased exponentially with the increase of corrosion rate. The interaction of corroded defects and fatigue loads was the primary reason for a sharp reduction of fatigue life of strand. Strand corrosion had more notable effects on fatigue performance than on static performance. Based on statistics analysis of experimental data, a constitutive relation and S-N curves equation of corroded strand were established respectively in monaxial tensile tests and fatigue tests.2. The static and fatigue flexural tests were carried on a batch of partial prestressed concrete beams to study the effects of strand corrosion on the mechanical performance of specimen beams. The static test results showed that strand corrosion not only transformed the ductile failure mode into a more brittle one, but also affected the cracking load of beams. In comparison with ultimate load, ductility of the beams were worst affected by strand corrosion. The fatigue test results showed that the fatigue failures of corroded beams were caused by the fatigue rupture of the corroded strands. The fatigue life and fatigue strength of specimens decreased with the increase of corrosion rate. After experimental statistics, a regression model between midspan deflection and cycle number, and a regression equation between concrete residual strain and cycle number were established, respectively. In addition, due to the effect of overloading on existing bridge structures, a novel prestressed concrete beam was tested under monotonic and cyclic loading to study the mechanic performances in this chapter. The results showed that this beam had satisfactory capacity and ductility both under monotonic and cyclic loading, thus it had a favorable application foreground. 3. On the basis of the internal force equilibrium and plane section assumption, a simple method based on the strain of concrete at the upper edge of compression zone was derived to calculate the midspan deflection and reinforced steel strain. The step increasing strain method was introduced to analyse the loading procedure of partial prestressed concrete beams with corroded strands in static test. The fatigue rules including constitutive relations and failure criterion of concrete at the upper edge of compression zone and reinforced steel (including prestressing strand) in tension zone were established. And on the basis of the rules, an analysis method for the fatigue damage process of beams was proposed according to the piece wise linear method and the step increasing strain method.4、The behavior of partial prestressed concrete beams with corroded strands in static tests were simulated to analyse the effect of strand corrosion on the mechanical performances of test beams by using ANSYS software. The simulation results were also compared with the experimental results. On the basis of Corten-Dolan accumulative damage rule and fatigue analysis module of ANSYS software, the fatigue life of partial prestressed concrete beams with corroded prestressing strands under three variable-amplitude loadings and different corrosion rates of strands were predicted equivalently.