# 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  
As described in Section 2.3, mechanical tests on the non-corroded and corroded steel bars were performed under dynamic loading imposing a gradually increased strain history (Figure 4). The main results of the mechanical tests under dynamic loading for each steel bar, in terms of total cycles to failure (Nf), strain at failure cycle (e\({}_{\text{u}}\)), maximum stress at failure cycle (\(\sigma_{\text{max,u}}\)) and maximum recorded tensile and compressive stress, (\(\sigma_{\text{max}}\)) and (\(\sigma_{\text{min}}\)) respectively, are summarized in Table 3.  
Focusing on the results of non-corroded steel bars, it was observed that there was a reduced bearing capacity in the maximum compressive load of about 25% in respect with the maximum tensile load, from 557 MPa to 447 MPa (average values), since buckling phenomena appeared due to the high L/d\({}_{0}\) ratio (free length in fatigue 240 mm to nominal diameter L/d\({}_{0}\) = 15). The dynamic response of steel reinforcing bars was degraded due to corrosion and the reduction degree of the bearing capacity was significantly dependent on the type of corrosion (uniform or pitting corrosion). In the case of low levels of corrosion damage up to 6% mass loss, there was no decrease in the number of cycles up to failure. However, a slight reduction in the strength capacity both for tensile and compressive loads was recorded in contrast to the non-corroded (reference) conditions; in detail, the percentage loss of maximum tensile stress dropped by 8.9% and the maximum compressive stress reduced by 7.1%, respectively. In the case of higher corrosion damage, characterized as pitting corrosion, a reduction in the number of cycles up to failure was observed, a fact that depends mainly on the maximum depth of pits and the effective diameter d\({}_{\text{eff}}\), which leads to a crucial residual cross-section [30; 31; 32; 33; 34; 35]. Similarly, significant degradation was denoted in terms of strength capacity, both in tensile and compressive branch. Particularly, the reduction in the tensile branch ranged from 10.7% up to 34%, whereas the reduction in the compressive branch ranged from 7.2% up to 29.9%. The degradation of mechanical properties was strongly related to the depth of the pits, since the effective diameter and the actually residual cross-section of corroded steel bar was significantly decreased, as already mentioned in the previous section. Moreover, the change in the reinforcing bar's surface around the pitting area caused an increase in the stress concentration, a fact that may be fatal for the load capacity of the material. Useful information concerning the dynamic response of corroded steel reinforcing bars could be extracted by an overall examination of the stress-strain curves. For this reason, representative stress-strain graphs of mechanical tests are cited in Figure 10.  
Figure 9: Reduction in the diameter in terms of the mean reduced diameter (d\({}_{\text{red}}\)) and the effective reduced diameter (d\({}_{\text{eff}}\)) in contrast to the nominal diameter (d\({}_{0}\)) in the function with mass loss of steel bars. Initially, when examining the stress-strain curves of the above-mentioned diagrams, it was observed that the non-linear hysteretic behavior of steel reinforcing bars differed from the mechanical response under monotonic (pseudo-static) loading. It was also obvious that for a constant strain amplitude of the strain history, the load-carrying capacity progressively decreased in each loading cycle, due to the high dynamic loadings that developed, which introduced fatigue effects in the material.