Behavior analysis of Unstiffened and Stiffened TubularJoints of Fixed Offshore

Welded tubular structures are widely used in offshore platforms. There is a high probability that these structures wreck down when subjected to cyclic loading in welded junctions. Although using internal rings within the junctions of metal jacket structures could efficiently lead to the reduction of stressconcentration in such structures, it increases the nominal stress, i.e. the stress in sections joined to junctions, and consequently reduces the fatigue life of the structure junctions. Now days, because of incremental human need in energy resources, especially oil recourses, using jacket structures composed oftube elements is very common. Therefore, because of vital role of such structures in oil industries, it is definitely important to construct structures with a higher fatigue life. In the present research, using the Ansys software, effects of both stiffener and without stiffener on the fatigue behavior of offshoreplatforms is investigated. To perform the calculations, we have modeled the whole platform in two situations, namely with and without stiffener, and the environmental loads including the sea waves and currents are included within the modeling. Comparison of the two situations reveals that the structures using the ring stiffeners not only reduce the hot spot stress, and consequently increase the fatigue life of junctions, but also improve the resistance (receptivity) of the structure.

کلیدواژه ها:

Offshore platforms ، Tubular joints internally ring-stiffener ، Finite elements