A new model for calculating the elastic local buckling stress of steel plates in square CFST columns

Abstract

Previous studies into the elastic local buckling response of the steel plates in concrete-filled steel tubular (CFST) sections have considered the effect of concrete infill on the plate boundary conditions and on the buckling mode shape (i.e. one-way buckling only), but have not considered the influence of hoop stresses. This is addressed in the current paper, where a new model is proposed in which the unloaded plate edges are assumed to be elastically restrained and account is taken of the influence of hoop stresses. Tensile hoop stresses are shown to delay the occurrence of local buckling in the steel plates of square and rectangular CFST sections, though their beneficial influence reduces with increasing rotational edge restraint. The model is verified against existing experimental results, revealing better predictions of elastic local buckling stresses compared to previous approaches. The influence of the key parameters — tensile hoop stresses, varying boundary conditions and differing width-to-thickness (b/t) ratios is subsequently explored using the developed model, where it is shown that the b/t ratio remains the dominant factor in defining the elastic local buckling stress of steel plates in CFST sections. Finally, an alternative equivalent thickness approach to allow for the influence of the hoop stresses is proposed.