Effects of External Pressure on Capacity of Tubular Beam-Columns

Abstract

The study reported in this paper has been motivated by the need for accurate estimation of tube capacity under combined loads due to axial force, bending, and external pressure. Unstiffened and ring-stiffened tubular members for offshore applications are analyzed using a rigorous finite-element technique, developed for the purposes of this research. The technique accounts for changes in the geometry of the tube, elastoplastic material behavior, longitudinal and cross-sectional imperfections, and residual stresses from the tube-manufacturing process. The computational results are compared with available experimental data as well as design equations, toward better understanding of tubular-member behavior. Of particular interest is the axial capacity reduction in the presence of pressure. For the unstiffened tubes considered, the ultimate thrust is nearly unaffected by pressure. However, stiffened tubes can be subjected to high levels of pressure that will, in turn, affect the maximum axial compression. The effects of pressure on the bending capacity are significant for both unstiffened and stiffened tubes.