## 4 Experimental Results and Their Analysis
### The Combined Effect of Longitudinal and Transverse Reinforcement  
The combined effect of longitudinal and transverse reinforcement on the concrete strength and deformability of reinforced, centrifuged concrete specimens were analyzed. The results of experiments performed on the test series C and the series B\({}_{A}\) are compared (Figures 7 and 8). As shown by the presented test data, the spiral reinforcement (Figure 4a) does not actually or only slightly (by a few percent) decreases the initial modulus of elasticity \(E_{ccir}\). It seems that the distance of 100 mm to 40 mm between the spiral coils does not significantly affect the conditions of the concrete mix formation and hardening when a coarse aggregate (up to 20 mm in diameter) is used. Coarse elements of the concrete fraction are easily pressed against the external wall of the mold, slightly retarding the development of small transverse compressive strains in the process of concrete curing. The decrease in coefficient \(\alpha_{1}\) is more influenced by the number of longitudinal bars than by the increase in their diameter. The number of longitudinal bars has a stronger effect on the coefficient's decrease than the increase in their diameter. The increase in the number of bars results in a more significant reduction of reinforcement mesh size than the increase in diameter of longitudinal bar. In the case under consideration the increase in the number of longitudinal bars from 6 to 12 (i.e., the increase \(\mu_{s}\) from 1.5% to 6.0%) decreases the coefficient \(\alpha_{1}\) to 10%. As a rule, a transverse (spiral) wire increases the elastic strains of reinforced, centrifuged concrete elements. The decrease in the pitch of transverse reinforcement, i.e., increase the confinement effectiveness (this is due to the restraint of transverse tensile strains) and the strength \(f_{cs}\) of reinforced concrete. Moreover, the compaction of longitudinal and transverse reinforcement leads to a more uniform distribution of loads in the wall of a centrifuged concrete element of annular cross section, which leads to fewer defects in the concrete structure and a relative increase in concrete strength. The relationship of the coefficient \(\alpha_{1}\) on the concrete strength is also apparent. Regardless of the spiral pitch, the increase in the concrete strength leads to the increase in the coefficient \(\alpha_{1}\). This can be explained by the fact that tensile stresses caused by shrinkage strains have a less negative effect on stronger concrete. From the graphs shown in Figure 7e-h, it can be seen that transverse and longitudinal reinforcement decreases the coefficient \(\alpha_{1}\) to 20%. Therefore, the total effect of transverse and longitudinal reinforcement on concrete strength due to various conditions of production and compaction or the appearance of a confinement effectiveness can be positive or negative. The combined effect of the longitudinal and transverse reinforcement on the strength and the initial modulus of elasticity of centrifuged concrete should be evaluating of the following formulae:  
\[\alpha_{1} = 0.78+s-\mu_{s}+0.002f_{c}\leq 1 \tag{18}\] \[\alpha_{2} = 1-\omega\left(\mu_{s}-\frac{0.1-s}{2}\right)\leq 1 \tag{19}\]  
Here \(\omega\) = 1-2.5 is the coefficient the value of which depends on the strength of concrete and on the ratio of longitudinal reinforcement \(\mu_{s}\); s is the pitch of the spiral. When \(f_{c}\) = 30 MPa to 40 MPa, \(\omega\) = 2, when \(\mu_{s}\)\(\leq\) 3.0% and \(\omega\) = 2.5 when 3.0% \(<\mu_{s}\)\(\leq\) 6.0%; in \(f_{c}\) = 40 MPa to 60 MPa, \(\omega\) = 1, when \(\mu_{s}\)\(\leq\) 3.0% and \(\omega\) = 1.5 when 3.0% \(<\mu_{s}\)\(\leq\) 6.0%. According to [2,17], longitudinal reinforcement of high strength (and a high value) added to the elements has virtually no effect on longitudinal strain \(\varepsilon_{\text{\tiny S1}}\), corresponding to the strength \(f_{\text{\tiny CS}}\) of reinforced concrete.