## 4 Experimental Results and Their Analysis
### The Combined Effect of Longitudinal and Transverse Reinforcement
The ratio of longitudinal reinforcement is \(\mu_{s}\)\(\leq\) 4.0% and the transverse spiral reinforcement pitch is \(s\) = 100 mm. The average value of the coefficient \(\alpha_{3}\) is equal to 1.0, while the spread of the experimental data are \(\pm\)10%. The transverse reinforcement has an effect on the value of longitudinal strain \(\varepsilon_{\text{\tiny S1}}\). Figure 7: _Cont._  
Figure 8: _Cont._  
Figure 7: Coefficients \(\alpha_{1}\) (**a**,**b**,**c**,**d**) and \(\alpha_{2}\) (**e**,**f**,**g**,**h**) dependence on the ratio of longitudinal reinforcement \(\mu_{s}\) by different pitch of transverse reinforcement. As shown in Figure 8e-d by lowering the pitch of transverse reinforcement, the strain, as well as the coefficient \(\alpha_{3}\) are increased. When the pitch of spiral reinforcement is decreased from 100 mm to 70 mm or to 40 mm the coefficient \(\alpha_{3}\) increases to 10% and 20%, respectively. The effect of concrete strength on the values of coefficient \(\alpha_{3}\) and longitudinal strain \(\varepsilon_{cs1}\) can be observed only for large values of the ratio of longitudinal and transverse reinforcement. When concrete strength decreases and the ratio of longitudinal reinforcement increases, the coefficient \(\alpha_{3}\) and the longitudinal strain \(\varepsilon_{cs1}\) are increased. Figure 8: Coefficients \(\alpha_{3}\) (**a,b,c,d**) and \(\alpha_{4}\) (**e,f,g,h**) dependence on the ratio of longitudinal reinforcement \(\mu_{s}\) by different pitch of transverse reinforcement. The correlation and regression analysis showed, the experimental strain can be expressed:  
\[\alpha_{3}\ =\ (1.3-3s)(1+\mu_{s})(1.15-0.0025f_{c})\geq 1 \tag{20}\]  
When the concrete of the compressed reinforced concrete element reinforced by high-strength reinforcement achieves the maximum strain, the external force taken over by the element continues to increase (Figure 4). The decrease in the spiral reinforcement pitch from 100 mm to 70 mm and 40 mm increases concrete compression strains from 15% to 20% and from 25% to 30%. When the ratio longitudinal reinforcement is small (\(\mu_{s}\)=1.5%) and the transverse reinforcement pitch according to structural requirements is \(s\) = 100 mm the concrete strains \(\varepsilon_{cs2}\) increase up to 10%, while for \(\mu_{s}\) = 5.5% and s = 40 mm they increased twice. The decrease in the concrete strength increases the strain \(\varepsilon_{cs2}\). In thin-walled elements, transverse reinforcement prevents bars of longitudinal reinforcement from losing their stability, thereby allowing the stresses transferred from the concrete to high-strength longitudinal reinforcement. It should be noted that the effect of stress redistribution is considerable when the longitudinal reinforcement takes over at least 30% of the compressive force. The pitch of transverse reinforcement and concrete strength decrease. The longitudinal reinforcement increase; the stress-strain, diagram for the concrete in its lower part becomes more even and is longer until the maximum bearing force \(N_{max}\) of the element is achieve. The expression of the coefficient \(\alpha_{4}\) depends on the mathematical expression of the stress-strain concrete diagram, the durability of the load and the parameters of the reinforcement of the structure. In addition, the degree of utilization of high-strength longitudinal reinforcement directly determines the size of strain \(\varepsilon_{cs2}\).