## 2 Reference Experimental Survey  
The reference experimental survey was performed at the Laboratory of the University of Rome \"Tor Vergata\", where four RC columns were cast and tested [27]. The specimens, with a height of 1800 mm and a 300 mm \(\times\) 300 mm square section, were reinforced with four \(\Phi\)16 mm longitudinal bars (Figure 1a). Two spacing values, equal to 250 mm and 300 mm, of the closed \(\Phi\)8 mm stirrups were considered. The concrete cover was equal to 30 mm. The elements were cast on a 1500 mm \(\times\) 750 mm \(\times\) 500 mm foundation (Figure 1a).  
For each of the two considered stirrups spacing, one column was kept un-corroded for reference (A), while a second one was subjected to a process of artificial corrosion of the steel reinforcement (B) at the column base. A 3% saline solution was contained in a PVC \(\O\)500 mm pipe, placed around the column and fixed to the foundation, up to a height of about 600 mm from the foundation extrados (Figure 1b). The longitudinal rebars were connected to the positive pole of the power supply (anode), while a \(\O\)10 diameter steel bar, placed inside the PVC pipe, acted as the cathode. A current intensity equal to 0.05 A for each bar was adopted. Table 1 shows the layout of the experimental program.  
Figure 1: (a) Column geometry; (b) artificial corrosion process.  
The effective corrosion amount and morphology were evaluated after the tests, by extracting the steel rebars from the specimens B25 and B30, characterised by stirrup spacing of 250 mm and 300 mm, respectively. Both the longitudinal and transversal reinforcements were corroded, and a sharp localization of the corrosive attack took place. In particular, even if the mass loss was about 24% in both the specimens, deep pits were observed in the longitudinal bars up to a diameter reduction of more than 30% in the specimen B25, and up to 50% in the column B30. The corrosion morphology played a fundamental role in defining the failure mode, as highlighted in the following.  
The test set-up is shown in Figure 2. An axial load equal to 300 kN was applied to the top column with a self-balanced system and with two high strength rebars, each one connected to a hydraulic jack. After the axial load application, a cyclic horizontal displacement history, with increasing amplitude, was imposed at a height \(h\) from the foundation extrados equal to 1.5 m, up to the failure. To this aim, an electro-mechanical jack was fixed to the load frame of the laboratory and linked to the column employing a hinged bar system, in which a load cell was placed. The loading history consisted of three complete cycles, for different values of the column drift, defined as the ratio between the horizontal displacement \(\delta\) at the load application point and the height \(h\).  
The experimental results in terms of load-horizontal displacements are summarised in Figure 3a, with reference to the columns A25 and B25, and in Figure 3b for specimens A30 and B30. In both cases, a decrease of the maximum load of about 30% was measured. A great influence of the corrosion can be observed in the shape of the cycle and then in the ductile behaviour of the elements. Mainly with reference to specimen B30 (sharply affected by very localised corrosion), the pinching effect can be clearly appreciated, due to the onset of brittle mechanisms. Further details can be found in [27].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Specimen** & **Stirrups Spacing** & **Corrosion** \\ \hline A25 & & - \\ B25 & 250 & \\ A30 & & - \\ B30 & 300 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Layout of experimental program.  
Figure 2: (a) Scheme of Test set-up; (b) test set-up.