Elastic limit state flexural–torsional postbuckling analysis of bars with open thin-walled cross-sections under axial thrust

This work deals with the elastic limit state flexural–torsional postbuckling analysis of simply supported bars with open thin-walled asymmetric cross-sections under axial thrust. As it is well known stocky bars with the above type of cross-sections always fail by flexural–torsional buckling in the case of asymmetric cross-sections (whose centroid does not coincide with the shear centre), while in the case of monosymmetric cross-sections the failure may occur either through flexural (Euler) buckling or flexural–torsional buckling depending on the geometric characteristics of the bars. In all the above three cases the critical state is associated with postbuckling strength. In this paper attention focuses on the first yielding occurring at the initial part of the post-critical path of flexural–torsional buckling. This is, in case of bars made from ideal elastic–ideal plastic material, associated with the maximum combined normal stress, due to axial compression, bending and warping, which, along with the nonlinear equilibrium equation, yield the maximum (ultimate) elastic load-carrying capacity. The elastic limit state postbuckling analysis given here is demonstrated with the aid of equal-leg angles commonly used in trusses.