In order to study the effects of the microstructure parameters of cement modified subgrade silty soil (CMSS) in a frozen area under freeze-thaw (F-T) cycles on the macroscopic mechanical properties, the static triaxial test, scanning electron microscopy (SEM), and grey relation analysis (GRA) were implemented on silty soil modified with 0% and 2% cement at optimum moisture content from the northwest in Jilin Province in China. The results showed that the shear strength, the cohesion of 0% and 2% CMSS, decreased with the increase of F-T cycles, while the internal friction angle was not obviously changed. The shear strength and its parameters of 2% CMSS doubled compared to that of 0% CMSS. The micro-parameters, representing the particle morphological characteristics, particle arrangement, and pore characteristics of CMSS, changed differently under F-T cycles. If the cement was not added, the cohesion and the internal friction angle were most sensitive to the average particle diameter (D_p) and the average particle abundance (C), respectively. When the cement content was 2%, the cohesion was chiefly affected by the particle size fractal dimension (D_ps), while the internal friction angle was mainly related to the average pore diameter (D_h). The main principle of cement improvement was to decrease D_h of soil under F-T cycles.

Introduction: In order to analyze the displacement and internal force of composite steel-concrete beams under the vertical load, The finite element solution of composite steel-concrete beams under concentrated loads considering the existence of interface slip and vertical uplift based on the basic idea of elastic mechanics was derived in this paper. Method: A new kind of stiffness equation of bar system was got and its correctness was demonstrated with experimental value, the problem of composite beams considering the existence of interface slip and vertical uplift was solved, avoiding to produce large amount of calculation with the body element method. Results and Conclusion: It can be seamlessly integrated into the current engineering design software, which provides effective help to practical engineering problems.

In response to the lack of clear calculation methods for the normal section bearing capacity of circular piers strengthened by concrete jacketing in current design codes, this paper derives a calculation formula applicable to the normal section bearing capacity of strengthened circular piers under unloading conditions. The derivation is based on the relevant provisions of the Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts, incorporating the plane-section assumption and ultimate state theory. Finite element verification shows that the theoretical values agree well with the simulation results, with a maximum error of –1.55 %, and the results are conservative, meeting engineering safety requirements. In terms of impact resistance, increasing the thickness of the strengthening layer significantly enhances the pier's stiffness, reduces the displacement peak, and shortens the dynamic response time, shifting the damage mode from global damage to locally controllable damage. Parameter analysis indicates that the diameter of the main reinforcement and the spacing of the stirrups have a limited effect on the displacement response but play a key role in energy dissipation capacity: increasing the main reinforcement diameter effectively improves the total energy dissipation, while reducing the stirrup spacing enhances the confinement effect on the core concrete and improves energy dissipation efficiency. Considering both economy and construction feasibility, it is recommended to prioritize larger diameter main reinforcement and control the stirrup spacing within the range of 10-15 cm in impact-resistant design to achieve an optimal balance between performance and cost. Combined with a bridge strengthening project in Changchun, this paper summarizes key technical points, forming a theoretically complete and practically verified technical system for pier strengthening.

The continuously reinforced concrete pavement force method was developed to obtain the analytical solution of stress and displacement in any part of a roadway. This method accurately calculates the displacement and stress of continuously reinforced concrete pavements at any point of the entire road section during the temperature reduction based on the bond-slip effect between reinforced steel bar and concrete, and considers the impact of foundation frictional resistance and the combined effect of cracks and restraint from the lug, In the practical example, under the temperature stress, the distribution of stress and displacement of reinforced steel bar and concrete was researched. The results show that it is necessary and reasonable to perform the force analysis of a practical situation during the entire road section.