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The time-dependent reliability assessment of ballastless tracks in service life is crucial for ensuring the safe and stability of high-speed railways. This work systematically compiles and summarizes the performance functions of ballastless track structures under different failure modes during service period, and then the all modes are regarded as a mixed series-parallel system, a regularization method for performance functions of multiple failure modes is proposed. Subsequently, the direct probability integral method (DPIM) is firstly introduced for evaluating the time-dependent reliability of the CRTS III slab ballastless track system. The accuracy and computational efficiency of the proposed method are verified through comparison with the traditional Monte Carlo method. Furthermore, the failure modes of the system are categorized into safety and applicability. Numerical examples demonstrate the generality and robustness of the developed method in system reliability analysis. The result indicates that environmental factors are the primary cause of diminished system reliability, both in terms of safety and applicability. Extreme temperature gradients are identified as a primary cause of safety performance degradation in track structures, while negative temperature gradients primarily contribute to serviceability deterioration. The mean of train load below 300 kN is essential for maintaining safety performance. The safety and applicability of the track structure after 30 years of service should be a key concern for the railway department. Especially, the reliability calculation method developed in this work for CRTS III systems can be extended to various static and dynamic system state evaluations.

The current technical standards primarily relied on experience to judge the interfacial bonding properties between the self-compacting concrete filling layer and the steam-cured concrete precast slab in CRTS III slab ballastless track structure. This study sought to enhance technical standards for evaluating interfacial bonding properties by suggesting the use of the splitting tensile strength to evaluate the impact of bubble defects. Specimens were fabricated through on-site experiment. The percent of each area of 6 cm 2 or more bubble defect was 0 in most of specimens. When the cumulative area of all bubble defects reached 12%, the splitting tensile strength value was 0.67 MPa, which exceeded the minimum required value of 0.5 MPa for ensuring bonding interface adhesion. Furthermore, when the cumulative area of all bubble defects reached 8%, the splitting tensile strength value was 0.85 MPa, which exceeded the minimum required value of 0.8 MPa, thereby overcoming the negative impact of each area of 10 cm 2 or more bubble defect. Additionally, keeping the cumulative area of each area of 6 cm 2 or more bubble defect below 6% ensured adequate bonding strength and reduced the occurrence of specimens with lower splitting tensile strength values.

CRTS III (China Railway Track System) slab track is a typical multi-layer composite structure. Door-shaped rebar is an important connecting component. Studying its service characteristics is crucial for disease prevention and control. To investigate the mechanical properties of door-shaped rebar under multi-factor coupling, a three-dimensional finite element model was developed and validated with full-scale tests. Then, considering the initial defects of self-compacting concrete (SCC), interlayer cracks and other damages, the mechanical properties of door-shaped rebar of a CRTS III slab track under temperature load were studied. The results show that under the action of an extreme temperature gradient, the maximum vertical displacement of the track slab occurs in the middle and corner positions of the slab with the positive temperature gradient, with displacement values of 0.87 mm and -0.99 mm respectively. Under positive and negative temperature gradients, the stress of the door-shaped rebar at the interface between the track slab and the SCC layer is 12.9 MPa and 16.5 MPa, respectively. When considering the conditions of the SCC slurry layer, the stress of the door-shaped rebar in the SCC layer under the action of a temperature gradient is generally in an increasing state. When there is a crack at the interface of the SCC layer, the stress of the door-shaped rebar unit in the crack area changes significantly, and the crack at the edge of track slab has the greatest impact on the stress of the door-shaped rebar under the positive temperature gradient, which is 157.9 MPa. The research results provide a theoretical basis for disease control.

This study proposes a frequency domain vehicle-track coupling model for the CRTS (China railways track system)-III type damping track system based on the two-dimensional vehicle-track-viaduct coupling model, and utilizes dynamic compliance method to determine the dynamic compliance for the vehicle and track systems. The accelerations for the viaduct are hereinafter obtained and are compared between CRTS-III damping track system and conventional CRTS-III track system, and the structure-borne noises for near field and far field of the viaduct are assessed with finite element method (FEM). The acoustic contribution rates for the substructures of the viaduct to the near-field and far-field noises are analyzed. The results reveal that in comparison with the conventional CRTS-III system, the CRTS-III damping track system can mitigate the viaduct acceleration peak with 69.9%, and mitigate the average acceleration with 60.4%. The near field and far field noise measurement points are captured for the CRTS-III damping track system, the sound pressure levels decline by 8.15 dB and 8.36 dB, respectively. The acoustic contribution rates for the viaduct top plate reach 65.28% and 68.30%, respectively. The viaduct top plate thus becomes the major noise source and the damping track system can effectively mitigate the structure-borne noise of the viaduct.