## 5 Concrete-Encased Steel Column Behaviors under Cyclic Loads  
In this section, a review of the recent study on the seismic and cyclic behavior of the CES columns is presented. In addition, the parameters that can have an impact on the seismic behavior of the CES columns, such as steel ratio, shear span ratio, axial load ratio, embedded depth ratio, steel shear connections, and concrete resistance are highlighted in detail. A large amount of CES column test data are gathered and reviewed in this paper from a recent decade's worth of research. Based on material composition, this review does not include stainless steel, steel fiber-reinforced concrete, recycled aggregate concrete, ultra-high-performance concrete, or engineered cementitious composite because of differences in material properties. The primary approaches applied to evaluate the seismic performance of CES columns in laboratory settings are low reversed cyclic loading and constant axial force. In order to simulate a seismic event, the CES column is first loaded axially to reach the target load ratio. After that, it is loaded horizontally with reversed displacement increments. An important performance indicator for evaluating energy dissipation capacity, load-bearing capacity, displacement ductility, stiffness degradation, capacity deterioration, etc., is the hysteresis curve (P-\(\Delta\)). CES columns typically fail in flexural mode, shear-flexural mode, and shear mode, depending on the primary design parameters. Figure 11: Three-dimensional N-M surface and 2D biaxial N-M curves obtained by fiber section analysis, (**a**) 3D interaction diagrams, (**b**) longitudinal direction cut from 3D interaction diagram, (**c**) latitudinal direction cut from 3D interaction diagram, reprinted with permission from [34], 2022, _Advances in Structural Engineering_. Figure 10: Axial–flexural behavior of CES column according to AJJ-2014 code [33], reprinted with permission from [30], 2019, _Construction and Building Materials_. In seismically active regions, the CES column's exceptional seismic performance is important. Due to this particular advantage, a significant amount of the present review has been conducted to examine the seismic behavior of CES columns using quasi-static loading, in which the column top is subjected to a low reversed cyclic horizontal force and a required axial compressive force. The shear span ratio, axial load ratio, stirrup arrangement, confinement ratio, shear connectors, and material strengths are among the important factors that have an impact on the seismic behavior of the CES columns [12]. According to the research study, when using a sufficient amount of steel, CES column specimens have remarkable cyclic strength and ductility [26]. CES column specimens, in particular, have a high load-bearing capability even after longitudinal bar buckling and spalling of the concrete cover. Based on these tests, the ultimate state and the restorable limit state were determined to be local buckling of the H-shaped steel followed by spalling of the concrete cover. The seismic behavior of 26 steel concrete composite columns under low cyclic reversed loading has been studied [36]. According to this study, under seismic load, the steel-concrete composite columns exhibit a bending failure mechanism. The deformation capacity is great, and the strength depreciation is modest. It demonstrates that the composite steel-concrete members have advantageous seismic behavior. As presented in Figure 12, all of the studied samples showed signs of bending failure, and the failure mechanism followed the standard procedures for bending failure members. Five CES columns that were designed to collapse in flexural tension or flexural compression have had their cyclic behavior examined experimentally by [37]. According to current seismic evaluation rules, CES columns with non-seismic detail and low axial loads controlled by flexural tension appear to meet the acceptance criteria.