American and European Hydrostatic Tubular Beam-Column Equation Comparisons

For structural design engineers, there is an apparent gap in how the hydrostatic pressure is treated between the American and European systems. In API RP-2A, the beam-column equations treat the axial and bending capacities the same as there is no hydrostatic pressure. This is physically not correct, as member utilization is a combination of hydrostatic, axial, and bending actions. In contrast, the ISO and NORSOK beam-column equations include reductions of axial and moment capacities due to hydrostatic effect. In this paper, available actual test data are compared with the API and ISO capacity equations. A third set of capacity equations provided by Chen et al. is also considered. Unity check (UC) results show that, although API equations lack the proper hydrostatic reduction in axial/bending capacities, it is compensated by the separate checks of hoop buckling and ultimate strength. For engineering applications, similar member designs will be obtained by either the European or the American systems.