# The Shear Behavior of the Curved Interface in Polyurethane-Concrete Composite Structures
## 3 Results and Discussion
### Effect of Arc Diameter on the Shear Behavior of the Curved Composite Specimens
#### 3.2.2 Shear Stresses of Curved and Planar Specimens with Different Arc Diameters  
The variation in shear strength with polyurethane density for composite specimens at four different arc diameters is illustrated in Figure 13. It is observed that as the polyurethane density increases, the shear strength of the composite specimens gradually increases, with a decreasing rate of increase. The trends in shear strength variation with polyurethane density are similar among specimens with different arc diameters, but the differences in shear strength increase slightly with higher polyurethane densities. For specimens with the same polyurethane density, increasing the arch diameter results in a gradual decrease in shear strength. The variation in shear strength with arc diameter for composite specimens at different polyurethane densities is illustrated in Figure 14. The shear strength of composite specimens with the same polyurethane density decreases gradually with increasing arc diameter; the rate of reduction decreases gradually. Specifically, when the polyurethane density is 0.66 g/cm\({}^{3}\), as the arc diameter increases from 400 mm to 500 mm, 700 mm, and 2000 mm, the reduction rates in the shear strength of the composite specimens are 8.23%, 20.18%, and 9.54%, respectively. Across different polyurethane densities, the reduction rates in the shear strength of the composite specimens remain generally consistent as the arc diameter increases, with similar trends observed in shear strength variation for the four arc diameters. For composite specimens with curved interfaces, smaller arc radii result in greater variations in peak shear strength, indicating that the diameter of the curved interface significantly affects the shear strength of the specimens. For specimens with the same arc diameter, shear strength increases with higher polyurethane density. The figure demonstrates that the trend of shear strength variation with arc diameter is highly consistent across different polyurethane densities, with shear strength decreasing progressively as arc diameter increases. The shear strength of curved composite specimens under different polyurethane densities and arc diameters is presented in Table 4. It is observed that there is a proportional relationship in shear strength among specimens with different diameters. Taking the shear strength of the planar specimen with a diameter of 2000 mm as a reference (weighted as 1.0), the shear strengths of curved specimens with diameters of 400 mm, 500 mm, and 700 mm are approximately 1.49 to 1.51 times, 1.37 to 1.39 times, and 1.09 to 1.11 times that of the 2000 mm specimen, respectively. For analytical purposes, these proportional factors are approximated to 1.5, 1.38, and 1.1, respectively. By fitting these proportional factors to the arc diameter, a relationship between the shear strengths of curved specimens and planar specimens can be determined, as shown in Figure 15. Based on this relationship, the shear strength of curved specimens with different diameters can be estimated using the shear strength of planar specimens as a reference. Figure 13: Variation in shear strength with polyurethane density for planar and curved composite specimens with different arc diameters. 3.2.3. Shear Moduli of Curved and Planar Specimens with Varying Polyurethane Densities and Arc Diameters  
The relationship curves of shear modulus with polyurethane density for composite specimens with different arc diameters and the relationship curves of shear modulus with arc diameter for composite specimens with different polyurethane densities are shown in Figure 16a,b, respectively. As illustrated in Figure 16a, the shear modulus of the specimens increases with increasing polyurethane density. Significant differences are observed between planar specimens (R1000) and curved specimens. Specifically, the shear modulus of planar specimens increases at an accelerating rate with increasing polyurethane density, while that of curved specimens decreases.