A theoretical analysis of the local buckling in thin-walled bars with open cross-section subjected to warping torsion

•Local buckling of thin-walled bars with open cross-section subjected to warping torsion was investigated theoretically.•A local critical bimoment was defined.•The local critical bimoment was determined on the basis of critical warping stress.•For bars with unsymmetrical cross-section, two local critical bimoments occur, which are different as regards the absolute value.•For bars with bisymmetrical and monosymmetrical sections, the determined absolute values of local critical bimoments are equal to each other.

Results of a theoretical analysis of the local buckling in thin-walled bars with open cross-section subjected to warping torsion are presented. The local critical bimoment, which generates local buckling of a thin-walled bar and constitutes the limit of the applicability of the classical Vlasov theory, is defined. A method of determining local critical bimoment on the basis of critical warping stress is developed. It is shown that there are two different local critical bimoments with regard to absolute value for bars with an unsymmetrical cross-section depending on the sense of torsion load (sign of bimoment). However, for bars with bisymmetrical and monosymmetrical sections, the determined absolute values of local critical bimoments are equal to each other, irrespective of the sense of torsional load. Critical warping stresses, local critical bimoments and local buckling modes for selected cases of thin-walled bars with open cross-section are determined.