Design of Vertical Chords in Deepwater Platform

Abstract

The effect of external hydrostatic pressure on the strength and behavior of fabricated steel tubular members is studied. The axial force is considered to be produced only by the applied external force but not by the pressure as is the case for the chords of offshore fixed platform. Column strength curves for columns loaded axially at the ends and column interaction curves for columns loaded eccentrically at the ends are obtained considering the influence of hydrostatic pressure. It is found that external pressure reduces the load carrying capacity of tubular columns significantly when the out‐of‐straightness and pressure are large. Also, sectional capacity is reduced significantly by the presence of external pressure when axial load is small. Design formulas are derived for axially loaded as well as eccentrically loaded columns by a simple modification of the present American Institute of Steel Construction (AISC) design formulas.