Investigation and formulation of LJF in collar-reinforced K-joints under OPB in jacket substructures of offshore wind turbines

Abstract

This study examines the local joint flexibility of collar-reinforced K-shaped tubular connections subjected to balanced and unbalanced out-of-plane bending moments. The accuracy of numerical models was first validated by comparing them with available experimental and numerical data. Following this, 274 finite element analyses were performed on 134 connections to investigate the influence of geometric parameters on the flexibility coefficient and the ratio of the flexibility coefficient in reinforced to associated unreinforced connections. The findings revealed that reinforcing K-shaped connections with collar plates significantly reduced the flexibility coefficient, with reductions reaching up to 90.41%, primarily due to the increased radial stiffness of the chord. Additionally, the results showed that longer and thicker collar plates led to a substantial decrease in the flexibility coefficient. Also, the effect of collar thickness becoming more pronounced as collar length increased, highlighting their combined contribution to improving connection stiffness. Moreover, the increase of β and decrease of γ result in the drop of the Local Joint Flexibility coefficient. Finally, two parametric formulas for calculating the flexibility coefficient in reinforced connections were proposed, demonstrating robustness and reliability, and providing consistency with industry standards across a range of connection configurations.