Probabilistic analysis of the SCFs in tubular T/Y-joints reinforced with FRP under axial, in-plane bending, and out-of-plane bending loads

Abstract

The stress concentration factor (SCF) is one of the most important parameters in the fatigue reliability analysis of tubular offshore structures. This parameter exhibits remarkable scatter which calls for more emphasis in accurately computing the SCFs for determining the fatigue life. As per the authors’ knowledge, no study has been conducted on the probability distribution of SCFs in tubular joints with FRP. Therefore, in this study, results of performing 288 FE analyses on 96 T/Y-joints with FRP have been used to propose a probability distribution model for SCFs in the FRP-reinforced joints subjected to axial, IPB, and OPB loads. According to the T/Y-connection FE models which were validated with several experimental tests, a set of SCF sample databases was generated. 11 various probability density functions (PDFs) were fitted to the relative frequency histograms of the SCF samples. For determining the parameters of every distribution, the maximum likelihood method was applied. Evaluating the goodness-of-fit according to the Chi-squared and Kolmogorov-Smirnov tests indicated that the Weibull distribution is the best one for the maximum SCF values in tubular T/Y-connections retrofitted with FRP under axial load. Also, the Gamma distribution was set as the governing probability function for T/Y-joints with FRP under IPB and OPB loads. In the final step, five fully defined PDFs were proposed for the maximum weld SCFs of in T/Y-joints with FRP under three different types of loadings.