## 4 Experimental Results and Discussion
### Monotonously Tested Specimens  
In total, seven column specimens were tested with a monotonic load. The specimens AB-NS-001-1, AB-NS-001-2, AB-NS-001-5 and AB-NS-001-6 are made with smooth reinforcement and have the same cross-sectional properties (same amount of reinforcement-central reinforcement 4 \(\times\)\(\mathcal{O}\)10 and corner reinforcement 4 \(\times\)\(\mathcal{O}\)8). The first two specimens were loaded with a force of 100 kN, while the other two specimens were loaded with a force of 150 kN. The specimens AB -NS-002-1 and AB -NS-003-1 were loaded with the same force of 125 kN, but had different diameters of the longitudinal reinforcement bars. The central cross-sectional reinforcement (4 \(\times\)\(\mathcal{O}\)12) is the same for both specimens. The corner reinforcement is different, it is 4 \(\times\)\(\mathcal{O}\)10 in the first specimen, while it is 4 \(\times\)\(\mathcal{O}\)8 in the second specimen. The last monotonically tested specimen with the designation AB-NS-004-1 was produced with ribbed reinforcement, 4\(\mathcal{O}\)10 as central reinforcement and 4\(\mathcal{O}\)8 as corner reinforcement. This specimen was loaded with an axial force of 100 kN. The geometrical properties and the type of longitudinal reinforcement of each column are given in Table 1, while the mechanical properties of each type of reinforcement are shown in Table 3.  
For monotonically tested specimens, the analyzed results of the moment and the rotation ratio showed a clear correlation. The main characteristic of all tested specimens is a high ductility due to the plastic deformation of the smooth reinforcement around the plastic joint resulting in a large displacement at the top of the column. The behavior of the column in three characteristic cross-sections of the monotonically tested column specimens is shown as the M/\(\varphi\) relationship in Figure 9.  
Experimentally obtained curves show three characteristic domains of the ratio of moment and rotation of the cross-section: the domain until the occurrence of the first crack  
Figure 9: Moment to rotation ratio for monotonously tested column specimens: (**a**) end section; (**b**) section at 150 mm height; (**c**) section at 350 mm height. (the initial part of the diagram where the curve of the ratio of moment and rotation for all samples coincides), the linear elastic domain until the occurrence of the cross-section yield (the part of the diagram from the beginning of the separation of the curves up to the beginning of the horizontal part of each curve) and the plastic domain up to the limit state of the bearing capacity of the cross-section (the horizontal part of the diagram). After the first crack has appeared, there is a significant separation of results for each sample. The reasons for this are differences in cross-section properties, material properties, and changes in axial force. When the yield strength of the reinforcement is reached, we move to the third domain of the diagram, which shows a small slope of the curve tangent for all monotonically examined samples. This relationship between moment and cross-section rotation is then continued until the specimen fails. From the ratio of moment and cross-section rotation it is clear that in the end cross-section and cross-section at a height of 150 mm there is a yield area, whereas in a cross-section at a height of 350 mm the yield area only occurred in two tested specimens (in one specimen AB-NS-004-1 with ribbed reinforcement and in one specimen AB-NS-001-2, which showed a different crack pattern). All tested specimens manufactured with smooth reinforcement have a pronounced plastic area that is five times or more larger than the elastic area. The influence of the axial force on the bearing capacity is also visible, as well as the influence on the rotation of the cross-section around the plastic joint. A higher axial force leads to a higher bending resistance of the cross-section, but also to a slightly lower rotation of the cross-section when reaching the final limit state.