# Structural Behaviour of Concrete Deep Beams Reinforced with Aluminium Alloy Bars
## 3 Results and Discussion
### Parametric Study
#### 3.2.1 Concrete Strength  
It is well known that the shear strength is directly influenced by the concrete compression strength. The effect of concrete compressive strength on the shear behaviour of AA RC beams was investigated by considering the concrete cylinder compressive strengths of 20, 30, and 40 MPa. To avoid flexural failure, four 14 mm diameter AA bars were used as both tension and compression reinforcement, as shown in Figure 7. Moreover, shear reinforcement consisted of 4 mm diameter AA bars at spaces of 100 mm and 133 mm at shear span and midspan, respectively. All beams had an a/d ratio of 2.28.  
Figure 6: Comparison of strain values obtained from tension reinforcement.  
Three beams with identical physical and mechanical properties but with different concrete strengths of 20, 30, and 40 MPa were numerically tested. All beams failed in terms of shear. The AA RC beam with 20 MPa concrete strength failed at a shear force of 124.1 kN. The beams with 30 and 40 MPa concrete strengths failed at shear forces of 156.8 and 181.4 kN, respectively. Figure 8 illustrates the relationship between concrete compressive strength (ranging from 20 MPa to 40 MPa) and the corresponding shear force capacity of numerically tested beams. The results indicated a clear trend in which shear force capacity increased with concrete compressive strength, confirming that higher compressive strength enhanced the beam's resistance to shear-induced cracking and failure.  
To compare AA bars with steel bars, the experimental results on RC deep beams reinforced with steel bars reported by [PERSON] [45] were included in Figure 9. The included  
Figure 8: Effect of concrete compression strength.  
Figure 7: Parametric study for concrete strength: (**a**) cross-section; (**b**) elevation.  
specimens had an a/d ratio of 2 and concrete compression strengths of 23 and 42 MPa. Two AA RC deep beams, which had the same a/d ratios and concrete compression strengths, were also numerically modelled for a fair comparison. Figure 9 compares RC deep beams reinforced with steel bars to AA RC deep beams. The relationship between the normalised shear stress and concrete compression strength is given in Figure 9 for RC beams reinforced with both steel [45] and AA bars. Normalised shear stress is given in Equation (9).  
\[Normalised\ Shear\ stress=\frac{V}{b_{w}*d*\sqrt{f_{c}}} \tag{9}\]  
where V is the shear force capacity at failure, bw and d are the width and effective depth of the beam, respectively, and fc is the concrete compression strength.  
The normalised shear stress for both RC deep beams reinforced with AA and steel bars increased from 0.71 to 0.74, with increasing concrete strength from 23 to 42 MPa. This demonstrated that AA and steel-RC deep beams had comparable behaviour once concrete compression strength increased or decreased. This result suggests that AA bars are preferable due to their corrosion resistance. It should be noted that the stiffness of RC deep beams reinforced with steel bars can be higher than those reinforced with AA bars due to the lower elastic modulus of AA bars (approximately 70 GPa compared to 200 GPa for steel).