Probabilistic analysis of the local joint flexibility in two-planar tubular DK-joints of offshore jacket structures under in-plane bending loads

Abstract

Tubular DK-joints are among the most common joint types in jacket substructure of offshore wind turbines (OWTs) and oil/gas production platforms. The local joint flexibility (LJF), as an intrinsic feature of a tubular joint, is one of the factors affecting the global static and dynamic responses of an offshore structure. In the present paper, a total of 324 finite element (FE) analyses were carried out on 81 FE models of two-planar tubular DK-joints under four types of in-plane bending (IPB) moment loads. Generated FE models were validated based on the available experimental data, FE results, and parametric equations. FE analysis results were used to develop a set of probability density functions (PDFs) for the LJF factor (fLJF) in IPB-loaded DK-joints. Based on a parametric FE investigation, a sample database was prepared for the fLJF values and density histograms were generated for respective samples. Nine theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov and chi-squared tests were used to assess the goodness of fit. Finally, the Birnbaum-Saunders model was proposed as the governing probability distribution function for the fLJF. After substituting the values of estimated parameters, four fully defined PDFs were presented for the fLJF in two-planar tubular DK-joints under four types of IPB loading.