Static Structural Studies on Reinforced Tubular T-Joints of Offshore Jacket Structures

Abstract

The oil discovery was one of the most important discoveries in the twentieth century. At the turn of the twentieth century, exploration started based on land-based resources and as the demands increased, the exploration was into sea-based resources. It started in shallow water and later in deep water regions. The jacket platform is the most commonly employed one in the shallow water depths. Stiffening is a reinforcing mechanism that essentially improves the strength as well as enhances the lifetime of the structures. Owing to greater mechanical properties and economic advantages, tubular structures are preferably used in offshore jacket structures. The present study investigates the stiffening effect on the behavior of static strength and stiffness of the tubular T joint of an offshore jacket platform structure subjected to axial compressive load. The tubular T model selected for this study, as per the API (American Petroleum Institute) standard, has the following dimensions: Chord length is 400 mm, diameter is 100 mm, thickness is 4 mm, and brace length is 200 mm, diameter is 50 mm, and thickness is 3 mm. The structural steel material with a Young’s modulus of 205 GPa and a Poisson ratio of 0.3 was considered for the analysis. The axial compressive load of 20 kN to 300 kN with an interval of 20 kN is applied on top of the brace section and the support conditions at the chord end are simply supported. Three-dimensional static structural analysis using the ANSYS software package was carried out to evaluate the effect of stiffeners placed over the chord section of the tubular T joint. An experimental program has been carried out in the laboratory, and the results are presented. A comparative study is conducted between the experimental and numerical for the validation of results. The stiffened configurations considered are: Can around the joint with 6 rings and 4 strips, Can around the joint with 6 rings and 6 strips, Can around the joint with 6 rings and 8 strips. For the given axial compressive load of 20kN, the joint stiffness of the unstiffened tubular T joint is 67.929N/mm. The stiffened configuration increases the joint's local stiffness by more than 100 percent, and a maximum of 140 percent is observed.