## 4 Experimental Results and Their Analysis
### The Impact of Longitudinal Reinforcement  
The results of the experimental studies samples series B, reflecting the effect of longitudinal reinforcement when the transverse (spiral) reinforcement pitch \(s\) = 100 mm are presented in Figures 5 and 6. As shown by Figure 5a,e, in most cases, the elasticity modulus \(E_{cs}\), of reinforced concrete is smaller than that of non-reinforced concrete \(E_{c}\). This shows that longitudinal reinforcement negatively affects the process of concrete formation. The larger the thickness of the wall, the larger the modulus of elasticity \(E_{cs}\) of the reinforced concrete, so that when wall thickness increases, the coefficient \(\alpha_{1}\) also increase. When the wall's thickness is greater than 70 mm (in fact, the wall thickness of the produced supports for the power transmission lines is equal from 50 to 70 mm) it is equal to 1.0. This shows that  
Figure 4: Coefficients \(\alpha_{ci\times 1}\) (**a**), \(\alpha_{ci\times 2}\) (**b**), \(\alpha_{ci\times 3}\) (**c**) dependence on the ratio of transverse reinforcement (when the coefficient of longitudinal reinforcement equal zero). for a sufficiently thick wall, i.e., with an adequate, thick interior and exterior protective layer of concrete, longitudinal reinforcement does not affect the modulus of elasticity of centrifuged concrete anymore. A negative effect of longitudinal reinforcement on the elasticity modulus \(E_{cs}\) seems to be caused by the limited compressive strains of the reinforced concrete elements in the curing concrete, causing high tensile stresses, which, in turn, leads to additional micro defects in the concrete. Further curing of the concrete under these stresses could not eliminate the defects which appeared in the structure of the curing concrete. The authors argue that there are two reasons for the increase in the coefficient \(\alpha_{s1}\) when the wall thickness \(t\) of the element increases and the ratio of longitudinal reinforcement \(\mu_{s}\) remains the same (Figure 5e). First, with the rise in the number of reinforcing bars, compressive strains are distributed more evenly and decrease by an absolute value. Second, the inner concrete layers of a tubular element are less constricted because the alignment radius of longitudinal reinforcement is constant for all the elements regardless of their wall thickness. Based on the performed statistical analysis, the formula presented below was proposed for calculating the coefficient \(\alpha_{s1}\) for assessing the effect of longitudinal reinforcement on the modulus of elasticity of centrifuged concrete:  
\[\alpha_{s1}\ =\ 1-8(\gamma-0.2)\mu_{s} \tag{16}\]  
where \(\gamma\ =\ \frac{\alpha_{s1}}{\alpha_{s1}}>0.2\) is the ratio of the external protective layer's value and the internal protective layer's value. This expression can be applied when the compressive concrete strength \(f_{c}\) varied from 25 MPa to 60 MPa and the ratio of longitudinal reinforcement \(\mu_{s}\) varied from 1.0% to 6.0%. The experimental data presented in Figure 5b,f show that the strength \(f_{cs}\) of the reinforced concrete specimens of annular cross section can decrease considerably compared to that of the strength \(f_{c}\) of the non-reinforced concrete elements. Only in some particular cases \(f_{cs}\) is larger than \(f_{c}\). It should be noted that when the amount of reinforcement increases, the thickness of the optimal wall also increases, although we see a decrease in the strength of the centrifuged concrete elements of annular cross section. Accordingly, the optimal wall thickness of the centrifuged concrete elements depends on technological as well as structural parameters. In the case of a very thin wall, the decrease in the concrete strength is more evident because premature breaking of the elements takes place due to the loss of stability of the reinforcing bars. When the amount of longitudinal reinforcement elements increases, the strength of reinforced concrete of annular cross section decreases (Figure 5f).