## 3 Results and Discussion
### Backbone Curves  
The backbone curves of all the column specimens are presented in Figure 9. The backbone curve reflects the relationship between the peak loads and the corresponding displacement at each drift ratio point. Based on the backbone curve, three stages can be observed: (a) the elastic stage, i.e., the straight line before reaching the yield point, (b) the elastic-plastic stage, i.e., nonlinear response, and (c) the failure stage, i.e., shear strength degradation after longitudinal rebar buckling. It can be seen from Figure 9 that the material properties, axial load ratio, and transverse reinforcement spacing had some impact on the overall response of the backbone curve. Specimens BMRC1 and NEWRC4 had distinct initial stiffness compared to other specimens. Hence, it can be concluded that before reaching the yield load, initial stiffness can be affected by material strengths and axial load ratio. Additionally, in Figure 9, a comparison is made between the backbone curves of the column BMRC1 and NEWRC1; it can be observed that the overall force-displacement response is similar between the two specimens. Hence, the primary objective of this study to achieve a similar force-displacement response with a reduced cross-sectional area and rebar volume with NEWRC1 was achieved. It can also be observed that the use of high-strength material enhances the initial stiffness, as BMRC1 is stiffer than NEWRC1. However, both specimens followed a similar pattern after achieving the peak load and failed due to longitudinal rebar buckling. The difference in the behavior of BMRC1 and NEWRC1 could be due to the combined influence of both concrete as well as steel, as reported by [33; 34]; therefore, future studies can focus on combining the HSC with NSR and NSC with HSR. Figure 8: Hysteresis loops of specimens: (**a**) BMRC1; (**b**) NEWRC1; (**c**) NEWRC2; (**d**) NEWRC3; (**e**) NEWRC4; (**f**) NEWRC5; (**g**) NEWRCF. A comparison between the backbone curves of the columns NEWRC1, NEWRC2, and NEWRC3 can be seen in Figure 9. Here, the backbone curves of all three specimens overlap before the column's yield load point, which indicates that the difference in transverse rebar spacing did not influence the initial stiffness. However, apparent differences can be observed in the elastic-plastic stage and failure process. The shear strength degradation in the specimens NEWRC2 and NEWRC3 was more rapid due to the longitudinal rebar buckling at an earlier drift ratio, thus indicating that NEWRC2 and NEWRC3 have poor ductility compared to NEWRC1. From Figure 9, a comparison is visible between the backbone curves of the columns NEWRC1 and NEWRC4. The maximum load of NEWRC4 is higher than that of NEWRC1 due to the increase in axial load ratio. There is an apparent difference in the initial stiffness between the specimen; NEWRC4 is stiffer than NEWRC1. For NEWRC4, after reaching the maximum load, a steeper descending branch and rapidly degrading strength can be observed, thus indicating poor ductility compared with NEWRC1. The ultimate drift ratio declines from 9% to 8% when the axial load increases. This is because a higher axial load exacerbates the compressive failure of core concrete, especially at the latter stages of loading. Furthermore, in Figure 9, the backbone curves of the columns NEWRC1 and NEWRC5 are compared with each other. The force-displacement relationship, initial stiffness, yield point, elastic-plastic response, and failure pattern for both the specimens are identical. Hence, the results suggest that the NSR and HSR transverse reinforcements can provide similar confinement under a low axial load. Therefore, it is advised to check transverse reinforcement spacing and axial load ratio from all the comparison results when designing high-strength bridge columns. Figure 9: Backbone curves: (**a**) All specimen; (**b**) BMRC1 and NEWRC1; (**c**) NEWRC 1, 2, and 3; (**d**) NEWRC 1 and 4; (**e**) NEWRC 1 and 5; (**f**) NEWRC. Additionally, in Figure 9, the backbone curve for NEWRCF is presented.