In biaxial bending, the compression zone of a concrete column naturally forms a curved, parabolic-like profile. As shown in the figure, the compression zone boundary emerges from the extreme compression fibre intersection point and curves toward the neutral axis (NA), responding to the combined bending about both principal axes. This parabolic compression zone does not run straight but instead follows the real stress distribution caused by the interaction of moments about the X- and Y-axes. The orientation of the neutral axis, inclined at an angle θ to the geometric axes, further influences the compression zone’s shape and extent along the breadth b and height h of the column.