## 2 Experimental Testing
### Test Setup and Protocol
#### 2.2.2 Measuring Instruments and Measured Parameters  
Several different measuring instruments were used during the test (Figure 6). Strain gauges were attached to reinforcing bars prior to concreting, LVDT extensometers were placed at characteristic locations on the outer surface of the column, LVDT measuring instruments were used to control the displacements of characteristic points and to measure the relative deformations of the end section, inclinometers were used to measure column rotation and dial gauges without electronic recording were used to cheque the displacement measurements. In addition to the above mentioned measuring instruments, LVDT was also installed in the presses and measuring doses to define the magnitude of the load and displacement of the press at each test step. Most of the measuring instruments were located near an expected plastic joint. Figure 5: Load input curves by displacement control; left: monotonous load; right: cyclic load. The stress level and deformation in the longitudinal reinforcement bars was monitored by strain gages installed during the concreting of the specimens. The position and number of the strain gages were not the same for each specimen. Since there were several parameters determined by experimental analysis, the strain gages were placed in the most suitable locations for recording the results of each parameter. All columns had built-in strain gages on the rebars in the area of the end section in the compression and tension zones. In most cases one strain gage is installed in the compression zone and two strain gages in the tension zone. For monotonically tested specimens, the compression zone of the cross-section is uniquely determined, whereas for cyclically tested specimens the compression zone is considered to be the one in which compressive stresses occur in the first load cycle. For monotonically tested specimens, which are marked AB-NS-001-2, AB-NS-001-6, and AB-NS-004-1, four additional strain gages were installed at the height of the plastic joint on the tensile reinforcement at distances from the end section of 100, 200, 250, and 300 mm. Cyclically tested column specimens marked AB-NS-001-4, AB-NS-001-8, AB-NS-001-9, AB-NS-002-2, and AB-NS-003-2 had strain gage pairs (compression-tension side) at heights of 100, 200, 250, and 300 mm. An additional stress level was monitored  
Figure 6: Positions of measuring spots. by a strain gage installed in the anchor foot just below the end section on the columns with the designation AB-NS-001-1; AB-NS-001-3; AB-NS-001-5; AB-NS-001-7; AB-NS-001-9; AB-NS-002-1-2; and AB-NS-003-1-2. HBM K-CLY4-0030-1-120-3-020-N strain gages with a 3 mm measurement base were used. Figure 7 shows the arrangement of the measuring devices near the plastic joint. The column AB-NS-001/18/9-9 is shown in this figure, as this column had the most measurement points. LVDT extensometers were placed at the level of the plastic joint formation on both sides of the column to measure the relative deformations. Strain transducers with a measurement base length of 100 mm were used. A pair of strain transducers were placed at the bottom of the column to measure the relative deformations near the end section of the column. Due to its dimensions, the measuring instrument cannot be placed at the end section itself, but 150 mm from the bottom of the column. A second pair of extensometers was placed at the level of the plastic joint, the position of which was obtained from the numerical analysis. This served to obtain the relative deformations at this point and to confirm the accuracy of the numerical calculation. From the experimentally obtained values of relative deformations, the cross-sectional rotations were calculated, but also, if found, the crack width around the measured base of the extensometer was recorded. The measurement of the displacement at the column top was performed with an LVDT instrument with a measured base of 250 mm. This displacement was also controlled by the LVDT installed in the horizontal press.