Pores of different sizes and quantities are formed during the molding process of recycled aggregate concrete (RAC). However, few studies have examined the individual and combined effects of porosity and mesoscale pore size (pore size) on the axial compressive mechanical properties of RAC. In this study, the influence of porosity and pore size on the axial compressive mechanical behavior of RAC was examined by incorporating expanded polystyrene (EPS) particles to create prefabrication of pores. Additionally, crack development influenced by pores was analyzed using high-energy X-ray computed tomography (CT). Gray correlation analysis was employed to quantify the influence of pore size and porosity on compressive mechanical parameters. Furthermore, the combined effects of pore characteristics were assessed by introducing damage variables. It was shown that the compressive strength, strength reduction, elastic modulus, and modulus reduction exhibited linear correlations with porosity and exponential correlations with pore size. Cracks within the specimen predominantly propagate through the pores or along their edges. The influence of porosity on both strength and elastic modulus is more substantial than that of pore size. Moreover, the deterioration in mechanical properties is more pronounced when small pore size is coupled with high porosity, compared to the combination of large pore size and low porosity.

In the research on the influence of pore structure on the macroscopic mechanical properties of concrete, the experimental method cannot realize the accurate control of the pore structure parameters, and the research based on the numerical simulation method is insufficient in the scientific simulation and parameterization of the complex pore structure. A new numerical concrete modeling method is proposed, which introduces the total porosity, pore gradation, pore size, and sub-porosity of each gradation segment to realize the accurate simulation and parameterization of the pore structure. Based on the control variable method, 25 concrete mesoscopic models with the same aggregate structure and different pore structures are established, and uniaxial tensile experiments are performed. The pore structure accelerates the process of damage expansion from the periphery to the center of the specimen and makes the damage inside the cement mortar more localized. There are obvious exponential function relationships of three pairs: total porosity and elastic modulus, PSSA and elastic modulus, and tensile strength and total porosity. There is an obvious quadratic polynomial function relationship between tensile strength and specific surface area. For specimens with the same aggregate structure and total porosity, the elastic modulus increases with the increase of the macropore content, and the tensile strength and elastic modulus are basically not affected by the average pore radius. The effect of pore space distribution and sub-porosity on peak strain is greater than that of total porosity, but no obvious regularity is shown. For pores with a radius in the range of 0.15–0.8 mm, the smaller the pores, the greater the effect of their porosity on the elastic modulus and tensile strength, and the less effect on the peak strain.

The secondary pre-processing development of Abaqus based on the Python program is carried out, and the mesoscale finite-element model of light-aggregate concrete is established at mesoscale. A Python program capable of batch insertion of cohesive elements is also developed to simulate discrete crack initiation and propagation behavior inside multiphase mesoscale heterogeneous structures. The whole mesoscale deformation process of light aggregate concrete is simulated under both uniaxial tension and uniaxial compression. A parametric study on fracture energy, mixed fracture energy ratio, cohesive stiffness, and shear strength of each mesoscale component is conducted. The influence of mesoscale fractures on the overall mechanical properties of light-aggregate concrete is investigated from the perspective of damage morphology and mechanical response. The results show that the mesoscale light-aggregate concrete model can effectively simulate the fracture damage process of light-aggregate concrete under uniaxial tension and compression by comparison with experiments. The increase of mixed fracture energy ratio can significantly enhance the deformation of light-aggregate concrete in the softening section, and the degradation of residual strength becomes slower. The increase of cohesive element stiffness of each mesoscale component of light-aggregate concrete decreases the peak tensile strain and peak compressive strain of light-aggregate concrete under uniaxial tension and compression. It enhances the elastic modulus of light-aggregate concrete. Among the mesoscale components of light-aggregate concrete, the compressive strength of light-aggregate concrete under uniaxial compression is most sensitive to the change of the ratio of shear strength to the tensile strength of mortar, the second is aggregate, and the interface transition zone is weakest.

An analytical procedure of dynamic interaction analysis of the straddle monorail bridge–vehicle coupling system is proposed in this paper based on the finite element method and energy method. The calculation procedure is programmed with VB language for the solution of the governing motion equations of the straddle-type monorail bridge–vehicle coupling system. The effects of speed, three kinds of loads and different radius of curvature on dynamic responses of the monorail bridge–vehicle coupling system are analyzed. The simulation indicates that vertical vibration amplitude of the track beam decreases while the lateral amplitude increases with the increase in the radius of the curvature; the maximum value in lateral and vertical direction is 0.075 and 0.43 mm, respectively; and the maximum amplitude (lateral and vertical) and acceleration (lateral and vertical) are 0.69, 0.046 mm, 0.15 and 0.62 m/s², respectively, at the speed of 80 km/h. The vibration amplitude (lateral and vertical) and vertical acceleration increase with the increasing load, and the maximum values are 0.041, 0.43 mm and 0.44 m/s², respectively. The lateral acceleration is not easily affected by the load conditions.