Joints in welded tubular structures are subjected to stress concentration which is an important parameter to be considered In the fatigue design of offshore structures. Stress concentration can be reduced by providing stiffeners at intersections of tubulars. Internally ring stiffened tubular T and Y joints were analyzed by finite element method to determine the optimum stiffener parameters and develop parametric formulae for determining stress concentration factors. Static tests were also conducted on nine steel tubular T and Y joints to study the effect of stiffening on SCF and ultimate strength. The experimental values of SCF compare well with the analytical values using the parametric formulae. The analytical and experimental investigations are discussed in this paper.
Offshore production of oil forms a major portion of total crude production in India. The offshore production is mainly In the Bombay High region in the west coast, while efforts are being made for production in the east coast also. Presently steel jacket platforms are being used in the Bombay High region In water depths up to 80 m. Jacket type platforms are fabricated using tubular members which are inter connected through welded joints. Joints in welded tubular structures are subjected to stress concentration which is an important parameter to be considered in the fatigue design of offshore structures. Maximum stresses occur at the Intersection of chord and brace members either In the chord or In the brace depending on the type of joint, its geometry, and loading. Stress concentration factor (SCF) is the ratio of the maximum stress at the joint to the nominal stress in the brace away from the joint. Fatigue cracks tend to initiate at the tubular intersections where the largest principal stresses occur and failures often occur at the nodes or joints of the tubulars.