One of the effective factors in determining the bearing capacity of composite columns is variable confinement levels of concrete in different areas of the cross section. Since there is a lack of sufficient literature in the field of steel-reinforced concrete (SRC) columns, the present study aimed at exploring various regions of concrete confinement and the impact of each region on the bearing capacity of SRC columns. Accordingly, an experimental program was carried out on six reinforced concrete column specimens, with two types of H-shaped and cruciform steel core sections loaded under three different eccentricities. Furthermore, a finite element model was developed via the ABAQUS software to explore the concepts and conduct numerical investigation, which was then verified against experimental results. In addition, a parametric study with a higher number of eccentricities compared to the test specimens was performed on these columns, and regions with high, moderate, and low confinement levels were specified. The load-bearing contribution of each of these concrete regions to the share of concrete in the load-bearing capacity of the entire column was then calculated. The results confirmed that with increasing eccentricity, the high confinement area of concrete decreased while the moderate confinement area increased. Finally, relationships were presented for calculating the confinement coefficients for the mentioned regions in terms of eccentricity.
