Offshore tubular T-joints reinforced with internal plain annular ring stiffeners

Although the use of internal ring stiffeners to enhance the strength of tubular joints is common practice in older platforms, no definitive guidance on the design of such joints is found in any of the major offshore design codes. This is the result of an acute lack of research in this area. In this paper, the findings of an analytical study on the strength of tubular T-joints with centrally located plain stiffeners under brace compression loading are presented. Data on the strength of 32 stiffened joints and their associated unstiffened joints were generated using a well-validated numerical model. It was found that the stiffening could accentuate chord bending failure and that strength prediction based on pure shear yield was grossly conservative. The influence of the various geometric parameters on stiffener strength was examined and the observed trends form the basis of an accurate predictive equation for the strength of the stiffeners, which was derived using regression analysis. A methodology for predicting the strength of stiffened joints based on the summation of the stiffener strength and the strength of the unstiffened joint is proposed.