Study On Fatigue Mechanics Behavior Of Prestressed Concrete Bridges

With the increase of axle load and axle load frequency, the fatigue performance of the medium and small span simple-surported prestressed concrete (PC) bridges on the existing line have been the key problem of evaluation of heavy-haul railway operation safety. In this paper, the32m-span prestressed concrete T-type girder on the usual railway was studied and a number of scale model beams were fabricated on the basis of the similarity theory. And a fatigue real-time testing system was built on the measurement of strain and vibration amplitude and the developments of failure patterns, and the beam vertical vibration amplitude, the stiffness and the strain variation of reinforcing bar and concrete with the cycle frequency of increasing fatigue were studied. The main research works include as follows:(1) Based on the fatigue test of a total of121/6-scale PC model beams, the fatigue failure mechanism and characteristics were analyzed, the law of fatigue damage evolution of the beam was revealed and the primary parameter of fatigue damage characterization was brought forward.(2) Based on the fatigue postcycle static bearing capacity test of a total of101/6-scale PC model beams, the fatigue postcycle static failure characteristics of PC beams were analyzed. And the variation law of evolution of the fatigue postcycle static bearing capacity of PC beams was revealed.(3) Based on the corrosion fatigue test of a total of91/6-scale PC model beams, an analysis was made about the PC beam fatigue failure mechanism and characteristics with corroded steel bars and the variation law of fatigue life of the beam varied with the corrosion rate was put forward.(4) The uniaxial constitutive of compression concrete and prestressing and nonprestressing steel bar was modified by introducing the damage variable to model the constitutive law of damaged materials based on the test study. And a fitting equation of the variation of neutral axis under fatigue repeated loading was obtained from the test data. On the fatigue failure criterion of materials, the traditional analytic method under static (monotonic) loading was introduced into full-range analysis of normal section stress of PC beam after cracking. (5)Accordind to the fatigue experimental research, the mid-span deflection and crack propagation of PC beams with the cycle frequency of increasing fatigue were studied. Two computation methods, damage beam model and fitting formula, were present. At the same time, the intensification factor expression of maximum crack width of normal section was put forward, and it was characterized by the fatigue cycle ratio of n/Nf, considering the effect of fatigue cycle number (n) and fatigue life (Nf) and may describe the law of three stages of fatigue crack propagation.