No abstract

To study the mechanical properties of the China Railway Track System type II (CRTS-II) ballastless slab track structure, a 1/4-scale specimen of a CRTS-II slab ballastless track-32-m standard prefabricated simply supported box girder bridge with three spans and two high-speed railway lines was developed. The mechanical properties of the structure under the action of daily natural temperatures were studied under the natural environmental conditions. The structural strain and relative interlayer displacements were analyzed. The results show that the temperature of the CRTS-II ballastless track-bridge structural system changes periodically every 24 h. The strain of the structural layers of the track system first increases and then decreases sinusoidally, and the internal strain of the track system lags along the vertical depth direction. The relative displacement between the layers of the ballastless track bridge structure system increases with the increase in temperature. The extreme value of the vertical relative displacement appears between the track bed and the bridge at section 1/4 in the span, so it should be paid attention to by the maintenance personnel. Due to the constraint of the shear slots, the structural strain and relative displacement at the fixed end near the shear slots are smaller than those at the sliding end. The mid-span deflection is the largest, and the overall deflection during the cooling phase is more significant than that during the heating phase.

To study the evolution of mechanical properties of steel rebars in the China Railway Track System Type II (CRTS II) ballastless track–bridge structural system under repeated train loads, a 1/4 scale three-span ballastless slab track simple-supported bridge structural system specimen was manufactured and subjected to a multistage fatigue test with 18 million cycles. The experimental results show that the strain amplitude of the steel bar changes proportionally to the fatigue stress amplitude, and there is an obvious strain increase in the loading stage 4, where the fatigue stress amplitude is the largest. During the test, the cumulative strain–amplitude ratio first decreases then increases. At the end of the test, the cumulative strain–amplitude ratio increases by 5.46% and 5.32%, respectively, at L/2 and L/4 sections. The load–strain curve of the steel rebar keeps the shape of an oblique straight line. The slope increases first and then decreases with a degradation at the end of the test of 5.14% and 4.82%, respectively, at L/2 and L/4 sections. The mechanical properties of the rebar are enhanced under the first three million fatigue loading cycles: this is the fatigue strengthening stage. The mechanical properties of reinforcement gradually degrade from the three millionth cycle to the end of the test: this is the fatigue damage stage. Finally, based on the material fatigue damage model and the multistage cumulative damage criterion, the change rule of the load–strain curve slope of steel rebars in the fatigue damage stage is obtained by finite element simulation. The simulation results agree well with the experimental data, proving the validity of the calculation method proposed in this paper.