Larger I generally means greater geometric resistance to bending about the stated axis, while Z links elastic bending stress to moment through stress = moment ÷ Z. Radius of gyration describes how area is distributed about an axis and appears in slenderness calculations. Area is relevant to mass per length and direct stress when combined with density or load.
None of these numbers alone gives a safe load. Material grade, member length, restraints, load direction, connections, local plate slenderness and safety factors matter. Sharp-corner formulas can differ from tabulated properties for a real cold-formed tube. For selection or construction, compare against certified section tables and have the complete design checked under the applicable standard.
A useful reasonableness check is to compare the hollow section with the solid outer square. Removing the centre must reduce area, I and Z, while all values should remain positive. As B approaches zero, the formulas approach the solid-square results. As B approaches A, area and stiffness approach zero. Radius of gyration behaves differently because it is a ratio of I to area; moving a smaller amount of material toward the outside can keep r relatively large even while total area falls.
When comparing alternatives, make sure every candidate uses the same axis, units and ideal-versus-tabulated basis.
