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Li J.-Z.,Central South University | Li J.-Z.,National Engineering Laboratory for high Railway Construction | Yu Z.-W.,Central South University | Yu Z.-W.,National Engineering Laboratory for high Railway Construction | And 2 more authors.
Tiedao Xuebao/Journal of the China Railway Society | Year: 2013

On the basis of the real time measurement system for fatigue tests of conventional strain gauges, the fatigue tests and corrosion fatigue tests of 19 PC specimen beams of the heavy-haul railway were made. The development of fatigue failure patterns and the law of strains changing with the number of repeated loading of the PC beams were studied. The sectional strain distribution and neutral axis variations of PC beams in the process of fatigue loading were emphatically analyzed. The results show as follows: After multiple cycles of repeated fatigue loading, under the action of the upper limit of static fatigue loads, concrete in the compression zone of PC beams remains in the stage of elasticity, stresses are related to strains linearly and the fatigue deformation modulus E is attenuated continuously by three stages; for non-corrosion PC beams, the larger the amplitude of fatigue loading, the more obvious the neutral axis variations which move straight up; for fatigue loading of the medium amplitude, a long stable period, occurs with the neutral axis positions, occupying about 75% ~85% of the whole fatigue life; no matter what value the upper limit of fatigue loads is, the height of concrete in the compression zone remains basically unchanged when common reinforcements at the beam bottoms are damaged by fatigue on condition that the lower limit of fatigue loads is the same; unlike non-corrosion beams that experience three main stages, the cross-sectional neutral axis of corrosion beams remains largely unchanged under repeated fatigue loading. The results are of good reference to nonlinear analysis on a complete process of fatigue damaging in PC beams of heavy-haul railways.

Li J.,Central South University | Li J.,National Engineering Laboratory for High Railway Construction | Yu Z.,Central South University | Yu Z.,National Engineering Laboratory for High Railway Construction | And 2 more authors.
Tumu Gongcheng Xuebao/China Civil Engineering Journal | Year: 2013

According to the test method of dynamic-static loading combination loading test controlled analysis, totally of 6 1/6-scale PC model beams on the heavy-haul railway were made and the mid-span fatigue deflection and crack propagation laws were studied. Test results indicate that the evolution of mid-span deflection and crack propagation with the cycle frequency of increasing fatigue of 32 m-span PC beams on the heavy-haul railway exhibits as three stages, i. e., the swift growth stage, the stable development stage and the abrupt change stage. After cracking, the mid-span deflection of the beam can be calculated by the superimposition of residual deflection and instantaneous deflection. The cracks include normal section cracks in the pure flexure part, the shear cracks in the flexure-shear part. The normal section crack appears in the stable stage of fatigue damage evolution while the shear crack doesn't emerge until the failure stage. According to test results of fatigue deflection, the two computation methods, damage beam model and fitting formula, were proposed. The calculation results show that the computation results agree well with the test results and the deflection magnification factor is about 20%~30% in the stable stage of fatigue damage evolution and while 80%~100% near the end of fatigue failure. Finally, the intensification factor indicating maximum crack width of normal section is put forward by the statistical method, which was characterized by the fatigue cycle ratio of n/Nf and used to consider the effect of fatigue cycle number (n) and fatigue life (Nf) and describe the law of three stages of fatigue crack propagation. The calculation results indicate that the maximum normal section crack width of PC beams with right mixed-reinforcement on the heavy-haul railway is about 0.50~0.55 mm at the moment of fatigue failure. The test data validates the proposed method is effective and can satisfy the needs of engineering.

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