On the Structural Design of Tubular Joints

Stresses in thin-walled tubular joints can be calculated with finite-element computer programs that employ ‘thin-shell’ elements. Such a program, designated SATE, has been developed specifically with the object of determining stress distributions in complex tubular joints as generally encountered in the offshore industry. The program has been applied to several joint geometries and good agreement has been observed between experimental and calculated results. The program thus provides insight into the structural design of tubular joints. Using the SATE program, the influence of changes in design of both unstiffened and stiffened tubular joints on the stress-concentration factor has been studied. In this context, the current API recommendations for simple tubular joint design are discussed. Calculations have demonstrated that in the design of large tubular joints, allowance should be made for membrane action rather than for bending of the chord and brace walls. Such an approach leads to joints of low stress concentration.