## 6 Test Results  
### Columns Hysteretic Response  
The hysteretic responses of the column P16B (ASB column) and columns R16-UHS and R16-UHP (the repaired RR columns) in terms of horizontal displacement of the column top and the corresponding base shear (BS) are given in Figure 11a-c, respectively. The maximum BS values (BS\({}_{\text{max}}\)) for the RR columns were similar to the one recorded on the ASB column; therefore, the repair strategy was able to restore the strength of the columns. There was no abrupt falling of the BS values during the entire displacement progression. Therefore, the connection and the new rebar segments could sustain low cycle fatigue demand and high displacement ductility requests (up to ~6-7).  
The area of the hysteretic cycles of the RR columns was wider than that of the ASB; there was no pinching of the cycles due to shear rupture. The steel or the polymer fibers added to the concrete jacket, improved the column seismic performance in terms of dissipated energy (Section 6.3) and guaranteed the column flexural failure mode (Section 6.7). The repaired column with polymer fibers (4% of volume fraction) showed very similar behavior to the one measured on the repaired column with steel fibers (2% volume fraction).  
The ultimate displacement (\(\Delta_{\text{u}}\)) may be assumed to be equal to the displacement that produced a decreasing BS value equal to 0.8 BS\({}_{\text{max}}\) after the peak value BS\({}_{\text{max}}\). The results recorded in the positive load direction are discussed in detail because worse degradation of the column behavior was evident in this direction. The reduction of the BS values to 0.8 BS\({}_{\text{max}}\) was not observed at the maximum applied displacement in the positive direction for each column. Therefore, the ASB and the RR columns showed at least the same displacement ductility as ca. 6. In fact, the yield displacement (\(\Delta_{\text{y}}\)) was equal to ca. 5 mm for each column because it depended on Equation (13) in [PERSON] et al. [67]:The column section diameter (D), the column height (H), and the yield stress of the steel rebar (\(\epsilon_{y}\)) were the same for each column.  
\[\Delta_{y}=\frac{1}{3}\cdot\phi_{y}\cdot\mathrm{H}^{2};\ \phi_{y}=2.35\epsilon_{y}/D \tag{13}\]  
The RR columns showed hardening behavior along line's' in Figure 11b,c greater than the one of the ASB column along the line's' in Figure 11a. This means that the displacement ductility (\(\mu_{A}=\Delta_{u}/\Delta_{y}\)) can be greater than the one of the ASB column. The repair strategy was able to restore and probably improve the displacement ductility of the RR columns.  
The RR columns had new rebar segments with the same steel mechanical properties, but with a reduced diameter. Therefore, the maximum force in the rebar under tension was smaller than in the original rebar under tension. As a consequence, the flexural strength and the maximum BS values of the RR columns should be smaller than that of the ASB column. The restored BS values can be explained by the contribution of the new concrete part (HPFRC jacket). In fact, the HPFRC concrete had high compressive strength (Section 2). Therefore, the compressed part of the section of the RR columns were shorter compared with the ASB columns. The inner lever arm length increased for the RR columns and balanced the rebar diameter reduction. As such, the flexural strength and the  
Figure 11: Experimental hysteretic response of: (**a**) the As-built column (P16B); (**b**) the repaired column by concrete jacket with steel fiber (R16-UHS); (**c**) the repaired column by concrete jacket with polymer fiber (R16-UHP) during the tests Tol and Tol \(\times\) 2; (**d**) Experimental envelope curve for each tested column.  
corresponding maximum BSs was similar to the ASB. This was reproduced numerically in the fiber analyses in Section 7.