Experimental study on stiffness degradation of Crts Ⅱ ballastless track-bridge structural system under fatigue train load

Abstract

In this paper, a 1:4 scale specimen of concrete box bridge with ballastless track was constructed. The deflection evolution and stiffness degradation of the Crts Ⅱ ballastless track-bridge structural system were studied by carrying out a multistage fatigue loading test with 1.8 × 107 cycles. The results showed that, first, no cracks were formed on the surface of structural system during the test, the dynamic and static deflection ratio of the mid-span section of the structure changed from 108.49% to 106.74%, and the dynamic deflection and static deflection ratio gradually decreased. The cumulative dynamic deflection ratio of the structure exhibited obvious characteristics of the “three-stages” of evolution of the structural fatigue mechanical properties. Second, the static stiffness of the structural mid-span section, which had the most significant change compared to that of the other sections, decreased by 23.82% after the fatigue test. The static stiffness of stage 2, which had the greatest number of cycles, decreased the most compared to that of the other stages. Third, the dynamic stiffness degradation rates of sections L/4, L/2 and 3L/4 of the structure were 18.99%, 19.25%, and 18.59%, respectively. The dynamic stiffness degradation of the structure exhibited the evolution law of “three stages”, and the dynamic stiffness of the structure decreased most significantly in the initial stage of the fatigue test compared to that during the other stages. Moreover, the theoretical results of the stiffness decreasing rate of the mid-span section of the structure were consistent with the experimental results, and the service life of the beam in the structural system was far beyond the design life under the fatigue train load.