In order to improve the accuracy and universality of the nonlinear viscoelastic-plastic mechanical behavior characterization method of asphalt mixture, a new criterion for the division of the creep process of materials was established based on the strain yield characteristics, and the coexistence mechanism of Viscoelastic–Viscoplastic strain was proposed in the subsequent yield phase; then, a viscoelastic element was constructed in the form of a parallel connection of two fractional viscoelastic elements based on fractional calculus theory, and its mathematical equations were derived; with novel viscoelastic elements, a constitutive model characterizing the whole creep process of asphalt mixtures was developed and its analytical expression was derived. The laboratory short-term creep test of Cement and Asphalt Mortar (CA mortar) and the simulation test data of asphalt mixtures from the references were used to verify the constitutive model. The results show that the creep constitutive model of asphalt mixture established in this paper has excellent fitting accuracy for different phases of the creep process of asphalt mixture under different stress levels, where the minimum fitting correlation values R² for CA mortar, asphalt mixture (applied to pavement engineering), and asphalt sand are 0.9976, 0.981, and 0.979, respectively. Therefore, this model can be used to provide a theoretical reference for the study of the characterization of the mechanical behavior of asphalt materials.

Plate bearings in existing small-span bridges for heavy-haul railways have exhibited corrosion, detachment, and surface cracks under large axle loads, making them inadequate for the “capacity expansion and renovation” of heavy-haul railways. Therefore, identifying new bearings suitable for small-span bridges and developing a rapid bearing replacement method tailored to the operational needs of heavy-haul railways are urgent priorities. This paper takes spherical bearings as an example and proposes a method for rapidly replacing plate bearings with spherical bearings. The bearing replacement tests of six simply supported beams were carried out to verify the effectiveness of the proposed method. Dynamic performance tests of bridges and bearings were performed before and after the replacement. A finite element model was established to analyze the effects of bridge span and pier height. The results show that the entire bearing replacement process for a span bridge could be completed within 4 h using the proposed method. Compared to plate bearings, spherical bearings could improve the lateral dynamic performance of both the bridge and bearings. However, the improvement decreases as bridge span and pier height increase. For 2.2 m diameter cylindrical piers commonly used in heavy-haul railways, the pier height with spherical bearings should be limited to 10 m.

In order to improve the accuracy and universality of the nonlinear viscoelastic-plastic mechanical behavior characterization method of asphalt mixture, a new criterion for the division of creep process of materials is established based on the strain yield characteristics, and the coexistence mechanism of viscoelastic-viscoplastic strain is proposed in the subsequent yield stage; Then, a novel viscoelastic element in the form of parallel connection of two fractional viscoelastic elements is established based on the theory of fractional calculus, and its mathematical equation is derived; With the novel viscoelastic element, a constitutive model characterizing the whole process of creep of asphalt mixture is established, and its analytical expression is derived. The laboratory short-term creep test of Cement and Asphalt Mortar (CA mortar) and the simulation test data of asphalt mixture from the references were used to verify the constitutive model. The results show that the constitutive model has good adaptability to the creep characteristics of different types of asphalt mixture under different stress levels.So, the model can used to provide a theoretical reference for the study of the mechanical behavior characterization of asphalt materials.

The guardrail is an indispensable part of ballasted track structures on bridges. In order to reveal its influence on the track–bridge interaction of continuous welded rail (CWR), the longitudinal resistance model of the guardrail fastener and its influential factors are established through tests. By taking a continuous girder bridge (CGB) for railways as an example, a stock rail-guardrail-sleeper-bridge-pier integrated simulation model is developed. The effects of the guardrails, installation torque of the guardrail fastener, and joint resistance of the guardrail under typical conditions are carefully examined. The research results indicate that the nominal longitudinal resistance of the guardrail fastener and the elastic longitudinal displacement of the rail prior to sliding approximately grow linearly with the growth of the installation torque. The presence of a guardrail can alleviate the track–bridge interaction in the range of the CGB, but exacerbate the interaction near the abutment with moveable bearings. This fact enables the abutment position to be considered as a new control point for the design of CWR on bridges. Considering the changing rules of the rail longitudinal force and rail gap, it is recommended that the installation torques of the guardrail fastener and guardrail joint are 40–60 N·m and 700–800 N·m, respectively. The recommended maximum longitudinal stiffness of piers for CGBs is evaluated. When the longitudinal stiffness of the pier for a CGB is lower than the recommended value, the influence of the guardrail can be neglected in the design of the CWR.

A novel prefabricated strengthening structure (NPSS) is proposed to improve the vertical stiffness and load-bearing capacity of existing short-span bridges for heavier axle-load trains passing through. The strengthening principle of the NPSS is revealed through theoretical derivation. A refined calculation model is prepared to investigate the effects of two important parameters on the structural behavior of the bridge, including the support stiffness and the installation location of the NPSS. The calculation model is also verified with four-point bending test of a bridge removed from a heavy-haul railway. With the calculation model and the response surface methodology (RSM), the functional relationships among the crucial mechanical indexes of the bridge and the two parameters of the NPSS are methodically established. Thus, the optimal values of the parameters are determined via a multi-objective optimization model and the analysis hierarchy process-fuzzy comprehensive evaluation method. Furthermore, the feasibility of the optimal parameters is appropriately verified based on simulations of the vehicle–track–bridge dynamics. The existence of the NPSS with optimal parameters could enhance the vertical stiffness of the bridge by 21.0% and bearing capacity by 19.5%. In addition, it could reduce the midspan dynamic deflection amplitude by 23.4% and vertical vibration acceleration amplitude of the bridge by 25.2%. The results of the study are expected to contribute to the capacity development and rehabilitation of existing heavy-haul railways with low cost and convenient construction without railway outage.

To characterize curing heat release and temperature evolution during interface damage repair in China Railway Track System (CRTS) II slab ballastless track, the curing kinetics and thermal properties of repair slurry for interface damage (RSID) were investigated. Non-isothermal differential scanning calorimetry (DSC) was conducted at four heating rates, and the apparent activation energy was determined using the Kissinger, Ozawa, and Starink methods. An n-order curing kinetic model and a two-parameter (m, n) autocatalytic curing kinetic model were established and compared. The specific heat capacity and thermal conductivity were determined using laser flash analysis (LFA), and corresponding temperature-dependent constitutive models were established. These material properties were incorporated into a three-dimensional transient heat transfer finite element model considering curing heat release, which was validated through curing temperature-rise experiments. The results show that the curing exothermic peak shifts toward higher temperatures with increasing heating rate. The average apparent activation energy obtained from the three methods is 55.21 kJ/mol. The two-parameter autocatalytic model provides better agreement with the experimental curing-rate curves than the n-order model, with R² values exceeding 0.960. The specific heat capacity increases approximately linearly with temperature, whereas the thermal conductivity exhibits an exponential growth trend. The simulated and measured temperature histories agree closely, with an R² value of 0.979, a peak temperature difference of 0.2 °C, and a difference of 3 s in the time to reach the peak. The simulated temperature field shows greater heat accumulation in the interior, with higher temperatures internally and lower temperatures near the boundaries. These findings provide material parameters and a thermal analysis basis for optimizing interface damage grouting repair processes in ballastless track and support subsequent analyses of thermal deformation and the development of measures to control secondary damage during repair.