A Probabilistic Model for Assessing the Ultimate Strength of Doubler-Plated Tubular T/Y-Joints

This study introduces a set of probabilistic models to estimate the ultimate capacity of offshore tubular T/Y-joints enhanced with doubler plates, subjected to axial compression, axial tension, and in-plane bending. A comprehensive finite element framework, validated against ten experimental benchmarks, was employed to perform 630 simulations covering a broad spectrum of joint geometries and loadings. The numerical modeling incorporated precise representation of weld regions and segment-wise contact definitions between the doubler plates and tubular members. Both material and geometric nonlinearities were considered in the static nonlinear analyses. A total of 24 probability density functions were statistically fitted to the simulation outcomes using the maximum likelihood estimation technique. The suitability of each distribution was evaluated through three goodness-of-fit criteria: Anderson-Darling, Chi-square, and Kolmogorov–Smirnov tests. The Johnson SB, Log-Logistic (three-parameter), and Generalized Gamma (four-parameter) distributions demonstrated superior performance for compression, tension, and bending, respectively. Complete analytical formulations for the selected distributions were provided, with P–P plots confirming the accuracy of the fitted models. The findings present a novel contribution to the probabilistic evaluation of doubler-reinforced joints and offer a rigorous tool for enhancing the structural reliability and design of tubular connections in engineering practice.