Slenderness effects in thin-walled I-section struts susceptible to local–global mode interaction

• Parametric study of validated analytical model of thin-walled I-section struts under axial compression.
• Ranges of local and global slenderness most vulnerable to modal local–global mode interactions identified.
• Increasing the joint rigidity between the web and flange reduces the vulnerable slenderness range.

A variational model that describes the nonlinear interaction between the global and local buckling of a thin-walled I-section strut under pure compression is presented and subsequently exploited. A parametric study is conducted for two limiting cases, where the flange–web joint is assumed to be pinned or rigid. For a chosen set of geometries, the most undesirable parametric spaces are identified for both global and local slendernesses, in terms of the strut length and the flange width respectively, where highly unstable behavior is observed in the post-buckling range. Practical implications are discussed in terms of the idealized design strength relationship.