# Effect of Corrosion on the Hysteretic Behavior of Steel Reinforcing Bars and Corroded RC Columns
## 3 Experimental Results and Discussion
### Stress-Strain Behavior of Steel Reinforcing Bars under Dynamic Loading
Regarding the mechanical behavior during the compressive loading of steel bars, taking into account the accumulation of material damage due to fatigue as well as buckling phenomena, a huge drop in the compressive load carrying capacity was encountered with the progression of the loading cycles of steel either for the uncorroded bars or for the corroded ones, taking into account uniform corrosion or localized pitting corrosion. For all the cases in Figure 10 under investigation, the strength (compressive) capacity was recorded approximately equal to 400 MPa during the initial loading by imposing small deformation values (in the elastic zone of the material), while thereafter progressively increasing the imposed deformations decreased the maximum recorded compressive strength rapidly to a value of approximately 100 MPa towards the latter loading cycles. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Steel Bar**} & \multirow{2}{*}{ \begin{tabular}{c} **Mass Loss** \\ **(\%)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Cycles** \\ **to Failure** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Strain** \\ **at Failure (\%)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Maximum Stress** \\ **at Failure (\%)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Maximum** \\ **at Failure Cycle** \\ \end{tabular}  } & \multirow{2}{*}{\ \begin{tabular}{c} **Transile Stress** \\ **(MPa)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Compression** \\ **Stress (MPa)** \\ \end{tabular}  } \\ \hline X1 & 0 & 52 & 2.5 & 348.6 & 552.4 & \(-441.4\) \\ X2 & 0 & 52 & 2.5 & 346.1 & 560.0 & \(-444.9\) \\ X3 & 0 & 52 & 2.5 & 349.3 & 556.6 & \(-447.6\)  
In the case of pitting corrosion, the aforementioned remarks displayed a higher rate of degradation of the steel bars and a decrease in their load-bearing capacity under dynamic loading. In addition, pitting corrosion created an irregular cross-sectional shape for the corroded bars. This created varying strong and weak bending axes along the bar which directly affected the buckling behavior of the corroded bars. As a result, corrosion significantly reduced the buckling capacity of corroded bars and may result in the change of the failure mechanism to fatigue failure of the steel. In particular, in all tests the failure area of the steel bars was expected to occur at the mid-free length, as the inelastic buckling of the steel dominates the induced material damage at this point. Notwithstanding, in pitting corrosion specimens, changes in the failure mechanism of the corroded steels were recorded, as the large geometric irregularity in the pitting areas, the significant reduction in the residual active area favored in these areas the accelerated propagation of the fatigue crack leading to the failure (Figure 11). Figure 10: Stress–strain curves for all cases of dynamic loading compared to the curve obtained from the monotonic loading: (**a**) dynamic loading of a non-corroded specimen toward monotonic behavior; (**b**) dynamic loading of a corroded specimen in the case of uniform corrosion toward monotonic behavior, (**c**) dynamic loading of a corroded specimen in the case of pitting corrosion toward monotonic behavior and (**d**) dynamic loading in the case of uniform corrosion in comparison with pitting corrosion. Modeling the Stress-Strain (\(\sigma\)-\(\epsilon\)) Behavior of Steel Bars under Dynamic Loading  
Taking into consideration the extracted stress-strain diagrams and the findings of the previous section, the non-linear hysteretic behavior of the reinforcing steel was simulated. In detail, from the analysis of all extracted stress-strain curves under dynamic loading, the hysteretic models of the steel were obtained for the following cases:  
1. non-corroded (reference);
2. uniform corrosion;
3. pitting corrosion.