Behavior of Internally Ring-Stiffened Joints of Offshore Platforms

As part of a larger experimental program on assessment and rehabilitation of damaged, internally ring-stiffened, steel tubular joints of offshore platforms, experimental investigation was carried out on undamaged, internally ring-stiffened tubular joints to study their behavior, determine their strength, and establish a benchmark. The paper presents, in detail, the experimental investigation carried out on tubular joints that are stiffened internally with three annular rings under axial brace compression loadings. The chord and brace diameters of the tested T and Y joints were 324 and 219 mm and their thicknesses were 12 and 8 mm, respectively. The tested joints are approximately a quarter of the size of the largest joints in the platforms built in a shallow water depth of 80 m in the Bombay High field in the Arabian Sea. Bending of the chord as a whole was observed to be the predominant mode of deformation of the internally ring-stiffened joints, in contrast to the ovaling and punching shear of the unstiffened joints. Strength of the internally ring-stiffened joints was found to be almost twice that of the unstiffened joints of the same dimensions.