# Experimental Investigation on Shear Behavior of Dune Sand Reinforced Concrete Deep Beams
## 6 Conclusions  
In this experimental and analytical study, the effect of various influencing parameters on the shear strength of nine DSRC deep beams was investigated. The applicability of four existing national codes was evaluated, and ACI was improved to predict the shear strength of DSRC beams. The following conclusions were drawn:  
* Compared to NRC deep beams, a small amount of dune sand can improve the load-carrying capacity and ductility of RC beams, but too much of it has the opposite effect. When the DS replacement rate was 30%, the load-carrying capacity and ductility of beams were 5.3% and 27.4% higher than that of NRC deep beams, respectively. When the DS replacement rate increased to 50%, the load-carrying capacity and ductility of beams were 5.9% and 3.5% lower than that of the NRC deep beams, respectively.
* The effect of shear span-to-depth ratio on shear strength of DSRC deep beams was similar to that of NRC deep beams. As the shear-to-span ratio increases, the shear load capacity decreases and the failure mode of the DSRC beam changes from bending shear to compression shear. Similarly, the effect of the stirrup ratio on the shear strength of DSRC deep beams was similar to that of NRC deep beams; the shear strength increased with an increase in the stirrup ratio.
* Relative to NRC deep beams, the shear strength of DSRC deep beams increased to a lesser extent with an increase in concrete strength. The shear stress in the specimens with concrete strengths of 40 and 50 MPa increased by 18.7% and 30.9%, respectively, compared to the shear stress in the specimens with concrete strength of 30 MPa.
* Based on the results of the statistical parameters, the selected four national codes give conservative prediction results. The shear strength predictions for both DSRC deep beams and NRC deep beams yielded by the ACI approach were closer to the experimental results than other national codes. For NRC deep beams, ACI318 yielded an average strength ratio and standard deviation of 1.15 and 0.31, respectively, with a COV of 29%, while for DSRC deep beams, ACI318 yielded an average strength ratio and standard deviation of 1.17 and 0.10, respectively, with a COV of 9%.
* As the effect of dune sand on the concrete strength and shear strength of RC beams were both considered, the modified ACI318 approach in this paper provided accurate predictions with a mean and standard deviation of 1.018 and 0.066, respectively, which shows that the proposed formula agrees well with the experimental results of the DSRC deep beams. The model proposed in this study may provide a reference for shear strength prediction of DSRC deep beams.
* It should be noted that these conclusion are obtained based on the test results from limited specimens with multiple variables. More deep and fine studies on the DSRC beams with different DS replacement rate are required in the further.  
Conceptualization, Z.G. and Y.Q.; methodology, Z.G.; software, Z.G. and X.L.; validation, Z.G. and Y.Z.; formal analysis, Z.G and X.L.; investigation, Z.G. and Y.Z.; resources, Y.Q.; data curation, Z.G. and Y.Z.; writing--original draft preparation, Z.G.; writing--review and editing, Z.G. and Y.Z.; visualization, Y.Q. and X.L.; supervision, Y.Q.; project administration, Y.Q.; funding acquisition, Y.Q. All authors have read and agreed to the published version of the manuscript.  
This study was financially supported by the National Natural Science Foundation of China (Grant No. 52268046).  
Not applicable.  
All data generated and analyzed during this study are included in this article.  
The authors declare no conflict of interest.