ABSTRACT

In the usual steel cylindrical beam-column analysis, the cross section of the tubes is assumed to remain the same during the entire loading history. However, at large deformations, significant local buckling or distortion may occur in thin-walled cylindrical cross sections. In this chapter, a simple kinematic model, similar to that of “plane section remains plane” in beam theory is proposed to describe the changing shape of the locally buckled or distorted cross section during loading. Based on this kinematic model, the moment-curvature relationships for locally buckled thin-walled sections are developed for monotonic and reversed loading. In kinematic model for cross sectional distortion, the locally buckled section is assumed to consist of an ideal shape with a flat, straight, distorted portion and a circular, distorted portion. In order to obtain the internal moment in terms of a given deflection, a relationship between the curvature and the displacement is needed.