Static behavior of stiffened CFST KK joints of offshore wind turbines under antisymmetric loading

Abstract

This study examines the static behavior of the critical joints of the new kind of offshore jacket foundations under antisymmetric loading by employing a combination of experiments, finite element analysis (FEA), and theoretical derivation. Three tests and 35 FEAs of stiffened concrete-filled steel tubular (CFST) KK joints are described. The introduction of a novel perfobond ring rib (PRB) as a stiffener, along with using a limiting fixture during loading to consider interactions among the four braces, are novelties of this research. Experiments compare the influence of stiffener rib forms (PRB and Perfobond Leister Ribs (PBL)) on the behavior of CFST KK joints, highlighting the superiority of PRB strengthening. However, the influence of the stiffener rib form on the stiffness of the CFST KK joints can be ignored. The properties of PRB-stiffened CFST KK joints are further investigated via validated FEA models, which introduce the modified Mohr-Coulomb (MMC) criterion to realize steel fracture damage. A parametric analysis is then undertaken to explore how variations in the joint's geometrical parameters, chord material strength, and thickness and quantity of the PRBs influence the punching shear capacity of PRB-stiffened CFST KK joints. Furthermore, a formula is presented for punching shear strength in PRB-stiffened CFST KK joints by employing the superposition method. Its predictions align well with both experimental and FEA results.