Development of a Probability Distribution Model for SCFs in Uniplanar Tubular KT-Joints of Offshore Structures under IPB Moment Loading

One of the crucial parameters in the fatigue reliability assessment of an offshore structure’s tubular joints is the stress concentration factor (SCF). Depending on the joint geometry and loading type, the SCF exhibits considerable scatter which emphasizes the significance of deriving its governing probability distribution function. In the present paper, results of 144 finite element (FE) stress analyses, verified against experimental measurements, were used to develop a set of probability density functions (PDFs) for the SCFs in uniplanar tubular KT-joints under four types of inplane bending (IPB) moment load cases. Based on a parametric FE investigation, a sample database was created for the chord-side SCFs of central and outer braces; and density histograms were generated for respective samples. Nine theoretical PDFs were fitted to the developed histograms and the maximum likelihood method was applied to evaluate the parameters of fitted PDFs. The Kolmogorov−Smirnov test was applied to each case to assess the goodness of fit. Finally, the Inverse Gaussian and Gamma models were proposed as the governing probability distribution functions for the central- and outer-brace SCFs, respectively. After substituting the values of estimated parameters, 10 fully defined PDFs were presented for the chord-side SCFs of central and outer braces in uniplanar tubular KT-joints under four types of IPB loading.