# Effect of Corrosion on the Hysteretic Behavior of Steel Reinforcing Bars and Corroded RC Columns
## 1 Introduction  
As is widely known, corrosion poses a real threat for reinforced concrete structures especially when they are located in coastal areas. Reinforced concrete (RC) structures designed and built before the entry of seismic codes represent a source of seismic risk due to their vulnerability. International guidelines and standards in force for the seismic design of reinforced structures demand nonlinear static push-over or dynamic analysis, especially in earthquake prone areas. The use of finite element models (FEM) is a functional tool for the engineering community to analyze and assess RC structures by means of columns and beams. One of the most popular models is a force-based nonlinear fiber beam -column element [1, 2], where each integration point is further discretized in fibers. These fibers are defined by their area along with the uniaxial constitutive laws of their materials, concrete and steel. However, their considerable limitation is their inadequacy to simulate the response of members under the corrosion damage. Besides the continuous exposure of coastal RC structures in a corrosive environment, in cases where structures are located in seismic prone areas, structures are additionally subjected to dynamic loads due to intense seismic events. Another shortcoming of the FE models is that they do not consider the loading history of steel reinforcement and the number of inelastic cycles, since they can limit the service life of the structure. Thus, the need to propose a reliable numerical model to predict the dynamic response of existing RC structures subjected to corrosion is a matter of urgency. Yet, most of the abovementioned models neglect the coupling effect of corrosion and fatigue degradation. In fact, the majority of existing building stock of RC structures in marine environments is threatened by aggressive environmental factors, as the corrosion of steel reinforcement can have detrimental effects on the structural integrity of RC structures, leading to premature unexpected failure. Corrosion agents drastically reduce the effective cross-sectional area of the reinforcing bar, alter its mechanical response and affect the bond between steel and concrete. Moreover, the corrosion damage of reinforcing bars was only restricted by the consideration of an average reduced area or a reduced yield strength criterion and not of reduced fatigue life or ductility loss. Hence, the abovementioned implications should be included in the FE models to obtain a reliable predictive model of the RC element behavior. The degradation of the hysteretic behavior of steel due to fatigue (via pinching factor modelling) has been investigated by numerous former studies, including the modelling of hysteretic loops of S400 grade steel [3]. Nevertheless, for the complete definition of the hysteretic response of the current two-phase B500c grade steel, the study of reinforcing bars of different diameters at various imposed strain amplitudes or in progressively increasing blocks and at different slenderness ratio values is required to insert the influence of buckling phenomena on the mechanical behavior. Furthermore, to establish the mechanical behavior of corroded steel bars, a large number of experimental tests are required, considering different levels of material damage and different geometries of the pits. To date, several researchers have attempted to study the cyclic behavior of corroded steel reinforcement and to improve finite element models and validate them via comparison with experimental results [4; 5; 6; 7; 8]. As is well known, the buckling of steel reinforcement in RC columns is the most common type of failure mechanism observed. During the last two decades, several studies have been conducted towards the development of buckling models for steel reinforcement and the simulation of buckling of steel reinforcing bars embedded in concrete [9; 10; 11; 12; 13; 14]. Moreover, few experimental studies have been conducted to assess the flexural behavior of corroded reinforced concrete beams [15; 16; 17].