## 4 Experimental Results and Discussion
### Cyclically Tested Specimens  
Cyclic load tests were carried out on eight column specimens. Figure 12 shows the hysteresis loop for one test column obtained through the ratio of the transverse load and the displacement of the column upper end. A gradual increase in the area of the hysteresis loop with an increase in the displacement cycle is visible, which results in greater energy  
Figure 11: Crack width and position around plastic joint in relation to column top displacement. dissipation. The low bond strength between reinforcement and concrete affects pinching effect. The gradual reduction in stiffness in each cycle is favorable in term of the seismic resistance of the columns. For cyclically tested specimens, the results were prepared in such a way that envelope curves were derived from the hysteresis curves, which connect the extreme values of the curves and thus define the relationship between moment and cross-sectional rotation, which can be analyzed further. As with monotonically loaded specimens, the diagram of the ratio of moment to rotation obtained here can be divided into three characteristic areas. In the second area, the results for each specimen differ due to the geometrical and material properties of the individual specimen and the amount of axial load. Figure 13 shows the behavior of a single column specimen in three characteristic cross-sections around the plastic joint area. Their analysis shows the influence of each parameter on the load bearing capacity and deformability of the column. The specimens AB-NS-001-3, AB-NS-001-4, AB-NS-001-7, AB-NS-001-8, and AB-NS-001-9 are made with smooth reinforcement and have the same cross-sectional properties. The longitudinal reinforcement in the central part of the cross-section is 4 \(\times\)\(\mathcal{O}\)10, while the reinforcement in the corners is 4 \(\times\)\(\mathcal{O}\)8. The differences are only in the applied axial load and the concrete properties, as they are not all from the same series. The first two specimens were loaded with an axial force of 100 kN, the other two with a force of 150 kN, while the last specimen was loaded with a force of 125 kN. For the first two specimens, the mean compressive strength of the concrete tested on cubes was 47.5 MPa, while the other three specimens were loaded with 36.0 MPa. The specimens AB-NS-002-2 and AB-NS-003-2 were loaded with the same axial force of 125 kN, but their geometrical and material properties of the cross-sections are different, as they are made with smooth reinforcement. As with the monotonically tested specimens of the same series, the differences are in the amount of the reinforcement. The longitudinal reinforcement in the middle of the cross-section is \(\mathcal{O}\)12 mm. In the first specimen, the corner bars are \(\mathcal{O}\)10 mm, in the second specimen these bars are \(\mathcal{O}\)8 mm. The concrete compressive strength test showed a small difference in the average compressive strength for both specimens, as they were not erected in the same series. The average compressive strength of 40.8 MPa was measured in the specimen AB-NS-002-2, while the compressive strength of 36.2 MPa was measured in the specimen AB-NS-003-2. The specimen AB-NS-004-2 is made with ribbed reinforcement. The reinforcement around the center of the cross-section is \(\mathcal{O}\)10 mm, while the corner reinforcement is \(\mathcal{O}\)8 mm. The average  
Figure 12: Hysteresis cycles in one of the specimens. compressive strength of the concrete cube is 36.2 MPa. The specimen was loaded with an axial force of 150 kN. A characteristic failure of all specimens occurs as crushing of the concrete in the compression area around the end section after large deformations of the tensile area due to the loss of bond strength between reinforcement and concrete and the yielding of the reinforcement.