# Effect of Corrosion on the Hysteretic Behavior of Steel Reinforcing Bars and Corroded RC Columns
## 3 Experimental Results and Discussion
### Validation of the Hysteretic Seismic Response of RC Columns via OpenSees  
The behavior of the column was modelled with a force-based nonlinear fiber beam -column element, which employed six integration points and each integration point was further discretized in fibers. The fiber section was further segmented into concrete fibers (confined core concrete and unconfined cover concrete) and steel fibers with a uniaxial stress-strain relationship. For the purposes of the present study, the material Concrete02 Material - Linear Tension Softening was chosen from the OpenSees library. This material generates concrete with a low tensile strength and was chosen in order to assess the deterioration of the concrete at the base of the column where tension and compression act in sequential order and cause the concrete cover to detach. Figure 17: Non-linear response of the non-corroded column [19]. Figure 18: Non-linear response of the corroded column [19]. For the steel reinforcement, the hysteretic steel material as extracted in the previous section was employed in order to exhibit the corrosive factor under dynamic loading. The selection of the trilinear model over the simple bilinear and Menegotto-Pinto model was performed as both the bilinear and the Menegotto-Pinto models are perfectly symmetric in the tensile and compression branches without taking into account buckling effects, while at the same time they do not take into account the loading history of the steel and the damage it has undergone. Furthermore, the bond slip of the longitudinal reinforcement at the column-foundation interface was neglected since the steel reinforcement was fully anchored to the concrete. Considering the hysteretic model of non-corroded steel reinforcement as described in the previous section, the non-corroded column simulated rather accurately the seismic response in the anion branch, as reflected in Figure 19. In the first drifts up to 3.5%, the model followed closely the degradation of bearing capacity per cycle due to cyclic loading. In the cation branch its response was very near to that of the experimental one, with the only relatively large divergence exhibited at the displacement corresponding to the maximum force, since the model overestimated it by 8%. Moreover, the total number of cycles to failure acquired form the model fully coincided with the corresponding experimental number. To conclude, the non-corroded model sufficiently simulated the cyclic behavior of the RC column, both in terms of force and displacement. The analysis of cyclic behavior of corroded RC column taking into account the hysteretic model of the corroded steel reinforcement for uniform corrosion was insufficient to demonstrate the experimental results of the corroded RC column, despite the reduced values of steel reinforcement's mechanical properties inserted. As observed from the diagram in Figure 20, it was obvious that the model overestimated the bearing capacity of the corroded RC column both in tensile and compressive loads. In detail, in the anion branch the value of the maximum force showed a 10% deviation from the actual value (from 50 kN to 45 kN), while in the cation branch the value of the maximum force differed from the experiment by about 8.5% (from 49 kN to 45 kN), deviation that was apparently improved compared to the anion branch. In the latter drifts, the force under which the failure occurred was 28.9 kN and was twice the value of the experimental one. Regarding the force recorded in the last drift before failure, the force, as in the anion branch, was well beyond the true value (62% higher). The abovementioned differences between the analytical model and experimental results were due to the consideration of a uniform type of corrosion, while in actuality the corrosion damage of embedded (in concrete) steel reinforcement is recognized as pitting corrosion. Figure 19: Non-linear response of the non-corroded column (model).