Probability density functions of SCFs in internally ring-stiffened tubular KT-joints of offshore structures subjected to axial loading

Abstract

The stress concentration factor (SCF) which is one of the critical parameters in the fatigue reliability analysis of tubular joints exhibits considerable scatter calling for greater emphasis in the accurate derivation of the probability functions governing the SCFs. As far as the authors can tell, 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. In the present research, data extracted from the finite element analysis of 108 models, verified against test results obtained from the experimental investigation, were used to propose probability distribution models for SCFs in internally ring-stiffened tubular KT-joints subjected to axial loads. Based on a 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 determine the parameters of fitted distributions. In each case, using a developed computer code, the chi-squared and Kolmogorov–Smirnov 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, three fully defined PDFs were proposed for the maximum weld-toe SCFs of central brace, compressive outer brace, and tensile outer brace in internally ring-stiffened tubular KT-joints subjected to axial loads.