Probabilistic analysis of stress concentration factors in tubular KT-joints reinforced with internal ring stiffeners under in-plane bending loads

• The SCF distribution in internally ring-stiffened tubular KT-joints was experimentally investigated.
• 108 FE models were generated for parametric SCF analysis of KT-joints under four types of IPB loads.
• Extracted data was used to propose six fully defined PDFs for the maximum SCFs.

In the present research, results from the finite element (FE) stress analysis of 108 models, validated using test data obtained from the experimental investigation, was used to propose probability distribution models for stress concentration factors (SCFs) in internally ring-stiffened tubular KT-joints under four types of in-plane bending (IPB) loads. The SCF is one of the crucial parameters in the fatigue reliability analysis of tubular joints. It exhibits considerable scatter which calls for greater emphasis in accurate derivation of its governing probability function. According to the knowledge of the authors, no comprehensive research has been carried out on the probability distribution of SCFs especially in stiffened tubular joints commonly found in offshore structures. What has been used so far as the probability distribution of SCFs in the reliability analysis of this type of joints is mainly based on assumptions and limited observations, especially in terms of distribution parameters. Based on a FE parametric study, a set of sample databases was prepared for the maximum central- and outer-brace SCFs; and density histograms were generated for these samples. Nine different probability density functions (PDFs) were fitted to these histograms. The maximum likelihood method was used to compute the parameters of fitted distributions. In each case, using a developed computer code, Kolmogorov–Smirnov and chi-squared tests were applied to evaluate the goodness of fit. Finally, the best-fitted distributions were selected and after substituting the values of estimated parameters for each distribution, six fully defined PDFs were developed for the maximum weld-toe SCFs of central and outer braces in internally ring-stiffened tubular KT-joints subjected to four different types of IPB loading.