Probability density functions of the DoB in tubular KT-joints of jacket-type platforms under out-of-plane bending loads

Abstract

The degree of bending (DoB) has a profound effect on the fatigue behavior of tubular joints commonly found in offshore jacket structures. Probability density functions (PDFs) of the involved random variables are necessary for the fatigue reliability analysis of jacket structures. The objective of present research was the derivation of PDF for the DoB in tubular KT-joints commonly found in jacket-type platforms. A total of 243 finite element (FE) analyses were carried out on 81 FE models of KT-joints subjected to three types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Based on the results of parametric FE study, a sample database was prepared for the DoB values. Thirteen 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 test was used to evaluate the goodness of fit. After substituting the values of estimated parameters, six fully defined PDFs were presented for the DoB at the saddle positions of the central and outer braces in tubular KT-joints subjected to three types of OPB moment loading.