# Experimental Investigation on Shear Behavior of Dune Sand Reinforced Concrete Deep Beams
## 3 Results
### Load-Displacement Behavior  
The load-displacement curves of the specimens are presented in Figure 7a-d. At the beginning of the test, the concrete was not cracked, the specimen was in the elastic phase, and the load-displacement curve showed a linear relationship. As the load increased until the specimen cracked, the slope of the load-displacement curve decreased with an increase in displacement. Eventually, the load increased until shear failure occurred, and the load-displacement curve showed a horizontal linear relationship during the failure phase, followed by a sharp drop. The load-displacement relationship for specimens with various DS replacement ratios is shown in Figure 7a. The load-displacement curve for the specimen CC1 was similar to that of the specimen A1. The initial crack load of the specimen CC1 was approximately 18% of the maximum load. The ultimate load and the corresponding displacement of the specimen A1 were significantly smaller than those of the specimen CC1, which were 94.7% and 72.6% of specimen CC1, respectively. Additionally, the slope of the load-deflection curve of specimen A2 before the initial crack load was significantly smaller than that of the other two beams. When the displacement was increased, the ultimate load and displacement of A2 were slightly lower than in specimen A1. These findings suggested that when the DS replacement rate was 30%, the bearing capacity and ductility of deep beams were greater relative to those of the NRC deep beam, while the opposite phenomenon occurred when the DS replacement rate was 50%. This is mainly due to the fact that the elastic modulus of concrete with a DS replacement rate of 50% is lower than that of ordinary concrete, resulting in poor resistance to deformation and reduced flexural stiffness of DSC. Besides, the lower tensile strength of DSC leads to weaker crack resistance and \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Beam**} & \multicolumn{2}{c}{**Initial Crack**} & \multicolumn{2}{c}{**Incline Crack**} & **Ultimate** & **Shear Stress** & **Failure** \\  & **Width (mm)** & **Load (kN)** & **Width (mm)** & **Load (kN)** & **Load (kN)** & **(MPa)** & **Mode** \\ \hline CC1 & 0.05 & 168.8 & 0.10 & 392.4 & 856.0 & 4.98 & S-C \\ A1 & 0.04 & 180.5 & 0.15 & 351.0 & 812.0 & 4.72 & S-C \\ A2 & 0.06 & 179.0 & 0.14 & 379.5 & 787.0 & 4.58 & S-C \\ B1 & 0.03 & 192.5 & 0.13 & 418.6 & 922.4 & 5.36 & B-S \\ B2 & 0.03 & 253.4 & 0.09 & 531.6 & 1179.0 & 6.85 & B-S \\ C1 & 0.04 & 156.4 & 0.12 & 361.4 & 782.0 & 4.55 & S-C \\ C2 & 0.02 & 127.0 & 0.13 & 335.4 & 715.0 & 4.16 & S-C \\ D1 & 0.03 & 100.9 & 0.11 & 323.0 & 721.0 & 4.19 & S-C \\ D2 & 0.03 & 201.6 & 0.40 & 452.3 & 944.0 & 5.49 & S-C \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of test results for specimens. bond strength of reinforcement than ordinary concrete, so the deflection of DSRC beams is greater than that of NRC beams. The load-displacement relationship for specimens with different shear span-to-depth ratios is shown in Figure 7b. Before the specimens cracked, the load-displacement curves of the three specimens were similar. The monitored cracking load range was about 20% of the maximum load. Before the diagonal cracking load was applied, all three beams had similar load-deflection curves. After the initial crack appeared in the beam, the slope of the load-displacement curve of B2 was significantly greater than that of the other two beams, and the slope decreased as the shear span-to-depth ratio increased. Specim B2 had the highest ultimate load of the three beams, measuring 588.3 kN. The ultimate loads of specimens B1 and CC1 were 21.0% and 27.7% of the specimen B2 ultimate load, respectively. The initial crack and corresponding displacement of B2 were slightly larger than those of the other two specimens, but the ultimate displacements were significantly smaller, and were 76% and 55% of those of B1 and CC1, respectively.