Q690 High-Strength Steel Circular Hollow Section Stub Columns Under Axial Compression: Local Stability and a Nominal Resistance Calculation Method

The local stability of Q690 high-strength steel circular hollow section (CHS) members under axial compression is an important consideration in cross-section sizing and resistance calculation. To characterise the combined effects of strain hardening and local buckling, this study proposes a piecewise method for calculating nominal cross-sectional resistance based on measured material properties and finite element (FE) parametric analysis. First, base-metal tensile tests were used to determine the material parameters. An FE model incorporating strain hardening was then established and validated against published Q690 CHS stub-column test results. Second, a parametric study of 115 CHS stub-column models was conducted to examine the effects of the diameter-to-thickness ratio on peak resistance and local deformation. The results show that local buckling increasingly limits the contribution of strain hardening as the diameter-to-thickness ratio increases. Under the adopted material and initial geometric imperfection conditions, the FE peak resistance equals the nominal cross-sectional yield resistance at an interpolated diameter-to-thickness ratio of 55.38. The proposed piecewise relationship is capped at the nominal cross-sectional yield resistance and describes the transition from yield-controlled resistance to local buckling reduction. The mean ratio of FE peak resistance to predicted nominal resistance is 1.018, with a coefficient of variation of 0.034.