# 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
Figure 16b shows that the shear modulus of planar specimens is greater than that of curved specimens, and the shear modulus of curved specimens decreases as the arc diameter increases. For composite specimens of the same shape, the shear modulus increases with increasing polyurethane density. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Arc Diameter (mm)**} & \multicolumn{5}{c}{**Polyurethane Density (g/cm\({}^{3}\))**} & \multirow{2}{*}{**Multiple Relation**} \\ \cline{2-2} \cline{5-7}  & **0.25** & **0.33** & **0.42** & **0.51** & **0.58** & **0.66** \\ \hline
400 & - & 1.622 & 1.901 & 2.131 & 2.306 & 2.448 & 1.49–1.51 \\
500 & 1.255 & 1.520 & 1.772 & 1.982 & 2.120 & 2.245 & 1.37–1.39 \\
700 & - & 1.201 & 1.413 & 1.568 & 1.694 & 1.801 & 1.09–1.11 \\
2000 & 0.906 & 1.091 & 1.280 & 1.427 & 1.544 & 1.627 & 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Shear strength of curved specimens with different diameters under different polyurethane densities (MPa). Figure 14: Variation in shear strength with arc diameter for planar and curved composite specimens with different polyurethane densities. Figure 15: Multiple relationships of shear strength between curved s and planar specimens. 2.4 Peak Shear Displacements of Curved and Planar Specimens with Varying Polyurethane Densities and Arc Diameters  
The variation in peak displacement with polyurethane density for curved specimens with different arc diameters and planar specimens is shown in Figure 17. It is observed that the peak shear displacement of both curved and planar composite specimens generally exhibits a linear decreasing trend with the increasing polyurethane density. However, significant differences remain in the rate of decrease in peak displacement between curved and planar specimens. For the curved specimens, the rate of decrease in peak displacement gradually slows with the increasing polyurethane density, showing little overall correlation with arc diameter. In contrast, the planar specimen peak displacement reduction rate demonstrates a gradual increase. This phenomenon is closely linked to the earlier-discussed variation in shear modulus of the composite specimens with polyurethane density. Additionally, it is found that with the increasing arc diameter, the peak shear displacement decreases gradually, indicating that larger arc diameters require less displacement for shear failure, making the composite material interface more susceptible to shear failure. Thus, curved specimens exhibit more stable interface performance and are relatively less prone to shear failure. The trend of peak shear displacement of the curved composite specimens with arc diameter under different polyurethane densities is shown in Figure 18. As the arc diameter increases, the peak shear displacement of the curved specimens gradually decreases. A  
Figure 16: (**a**) Variation in shear modulus with polyurethane density for planar and curved composite specimens with different arc diameters, and (**b**) variation in shear modulus with arc diameter for planar and curved composite specimens with different polyurethane densities. Figure 17: Variation in peak displacement with polyurethane density for planar and curved composite specimens with different arc diameters. higher polyurethane density results in smaller peak shear displacement, consistent with the shear performance characteristics of polyurethane grouting materials of different densities [31]. This indicates that the peak shear displacement of curved composite specimens is primarily influenced by the properties of the polyurethane material. 2.5 Shear Residual Strengths of Curved and Planar Specimens with Varying Polyurethane Densities and Arc Diameters  
The variation in shear residual strength for the curved composite specimens with polyurethane density and arc diameter is shown in Figure 19. As seen in Figure 19, the shear residual strength of the specimens increases linearly with a higher polyurethane density.