In oil and gas industry, jacket structures are commonly used in shallow to moderate water depth to support drilling and production facilities. The jacket structures especially joints are subjected to cyclic loads from wind and waves and require special attention for fatigue induced cracks. Thickened cans are normally used in such locations to reduce the local deformation and associated hot spot stresses and in some cases use of internal ring stiffeners have been employed as a substitute to limit the large thickness at joints. Performance of such ring stiffeners at the joints against local deformation has been established and empirical equations to determine the stress concentration factor (SCF) at the brace chord intersection has been in use developed by Lloyds Register. However, the SCF at the Brace Ring Intersection (BRI) has not been well established, leading to failure of joint. Hence a comprehensive study involving large number of linear finite element simulations for varying parameters of chord, brace and rings have been carried out to obtain database of SCFs at crown, saddle and BRI locations and validated by experiments. Parametric study has been carried out considering slenderness ratio (γ), diameter ratio (β), thickness ratio (τ), depth ratio (η), and thickness ratio of ring (τr). Set of empirical equations have been developed using power regression model to calculate the SCFs at BRI locations in addition to Brace Chord intersection.
KEYWORDS: Jacket platform, tubular joints, ring stiffeners, Stress concentration factor, finite element method, axial loading.