## 4 Experimental Results and Discussion
### Monotonously Tested Specimens
This can be seen from a comparison of monotonically tested columns loaded with an axial force of 100 kN (AB-NS-001-1) and columns loaded with a force of 150 kN (AB-NS-001-5). These specimens have the same cross-sectional properties but different axial force levels. Besides the influence of the axial force, the influence of the amount of the longitudinal reinforcement is also clearly visible. The samples AB-NS-002-1 and AB-NS-003-1 were produced with different diameters in the corners of the column (AB-NS-002-1: 4 \(\times\)\(\Phi\)10, AB-NS-003-1: 4 \(\times\)\(\Phi\)8), whereby a larger amount of reinforcement is expected to increase the load-bearing capacity of the column. These two specimens were tested with the same axial force (125 kN) and were erected in the same series so that their concrete properties are the same. It should be noted that in addition to the amount of horizontal force and the amount of reinforcement (diameter), there are also differences in the mechanical properties of the installed reinforcement. In order to compare the influence of the different types of reinforcement, the results of the experimental testing of three specimens, which were carried out with the same amount of reinforcement, are compared. Specimens AB-NS-001-1 and AB-NS-001-2 were made with smooth reinforcement, while specimen AB-NS-004-1 was made with ribbed reinforcement. The same axial force (100 kN) was applied to all three specimens by experimental testing. When examining the moment to rotation ratio of the end cross-section, we can see that the specimen made with ribbed reinforcement can reach a limit moment almost 40% higher than the specimen with smooth reinforcement with the same properties. The same can be concluded by observing the other two cross-sections in which the relative deformations have been measured, thus determining the ratio of moment and rotation of the cross-section. From this it can be concluded that the specimen made with ribbed reinforcement has a higher load bearing capacity than the specimens made with smooth reinforcement. It should be emphasized that by testing the compressive strength of the concrete on cubes of specimens made with ribbed reinforcement, the mean compressive strength was determined to be 36.2 MPa, while the same was determined for specimens with smooth reinforcement at 47.3 MPa. From this it can be concluded that the load-bearing capacity of the specimen would have been even higher if it had been made from the concrete with the same properties as those of the two specimens made with smooth reinforcement. If we compare the end cross-sectional rotations of these specimens, we can see that a specimen made with ribbed reinforcement has a significantly lower value of cross-sectional rotation on failure than specimens made with smooth reinforcement with the same geometrical properties and the same level of applied axial force. However, if we look at the rotation of other measured cross-sections along the height of the ribbed reinforced specimen, we can see that a slightly higher value of rotation was measured at failure than for smooth reinforced specimens. From this we can conclude that the cross-sectional rotation is more evenly distributed over the height of the member in the ribbed reinforcement specimen than in the specimens made with smooth reinforcement where the dominant rotation occurs in the end cross-section and in the cross-section where the first crack occurs. Most of the monotonically examined specimens made with smooth reinforcement do not show a clear boundary between the areas in the diagram. If one considers bending moment and section rotation ratio for all tested specimens, it is not possible to determine the beginning of the reinforcement yield clearly. The reason for this is the loss of bond strength between the concrete and the reinforcement, which significantly influences the cross-sectional rotation. The gradual reduction in the stiffness of the element makes it difficult to detect the appearance of the first crack.