Mode interaction in thin-walled I-section struts with semi-rigid flange–web joints

Author-Highlights•Analytical study of elastic I-section struts under axial compression.•Non-linear variational approach developed to model local–global mode interaction.•Parametric study of different flange–web joint rigidities is presented.•Cellular buckling effect is reduced with greater joint rigidity.•Comparisons with finite element models are very good.

A recently developed variational model that describes the non-linear interaction between the global and local buckling of a thin-walled I-section strut under pure compression is extended to include semi-rigid flange–web connections. A formulation combining the Rayleigh–Ritz method and continuous displacement functions is used to derive a system of differential and integral equilibrium equations for the structural component. Cellular buckling, observed in the case where the web is assumed to provide no more than a simple support to the flanges, is found to be rapidly eroded by increasing the connection rigidity, although the local buckling wavelength still reduces as the post-buckling deformation is increased. The model is validated using finite element analysis; the results compare very well particularly when a high rigidity between the section web and flanges is simulated.