## 5 Concrete-Encased Steel Column Behaviors under Cyclic Loads
However, the high axial loads controlled by flexural compression and the lack of seismic details in CES columns make them deficient for current seismic assessment acceptance standards [37]. These results show that the presence of the steel section in the concrete column helps to improve the seismic behavior of the CES column even with no additional seismic consideration for the rebars and the stirrups. It appears that one of the key elements impacting the seismic performance of CES columns is the shear span ratio. While numerous elements influence the damage pattern collectively, an increase in span ratio tends to shift the damage from a shear-dominant  
Figure 12: Flexural failure of the four studied specimens, **(a,b)** cover spalling, **(c,d)** reinforcement buckling, reprinted with permission from [36], 2014, _Journal of Structural Engineering_. failure to a bending-dominant failure. The outcome shows that the shear span ratio and the slenderness ratio have a significant impact on the behavior of CES columns. According to [38], ductility increased, and the failure process slowed down as the ratio of shear span increased. The long columns' carrying capacity decreased as the ratio of slenderness increased, yet the chance of an abrupt collapse increased [39]. Table 1 summarizes some related previous research regarding the seismic behavior of the concrete-encased steel bridge piers. It shows the name of the authors, the year of the study, the type, and the achievement of analysis. One of the other most important factors affecting the cyclic behavior of the CES columns is the axial load ratio. Many researchers have examined the impact of this parameter. The capacity of energy dissipation, ductility, carrying capacity, stiffness degradation, and axial load distribution on the column are all impacted by the axial load ratio. A significant influence on the hysteresis behavior was the ratio of the applied axial compressive load [12]. Because of a significant increase in the moment of secondary bending caused by the axial loads, the columns appeared to have less capacity for energy dissipation and displacement ductility when the applied axial load was 40% of the ultimate load, as opposed to the columns with 20% of the axial ultimate load [22]. The carrying capacity, damage pattern, and deformation ability of the high-resistance CES columns are all impacted by the axial load ratio. The axial load ratio was the most influencing factor on the ductility of columns [38]. The axial compression ratio has an impact on the seismic resistance behavior of CES columns with high-strength concrete [39]. This has a detrimental influence on the deformation capacity and the energy dissipation capacity [41]. Furthermore, a larger load ratio is shown to reduce energy dissipation and deformation capacities [6]. However, a high load ratio increases the longitudinal reinforcing bars' dowel action and prevents the spread of oblique shear cracks, increasing the load-carrying capacity to some degree [41]. Regarding the impact of shear studs, it was found that while they improve the deformation capacity and lessen stiffness degradation, they do not affect the