Nonlinear behaviour of fully grouted CHS X joints and associated representation for overall frame analysis

• Published in: Thin-walled structures Vol. 152; p. 106761
• Main Authors: Zhang, Wei, Sang Choo, Yoo, Yang, Peng, Shen, Wei, Huang, Zhenyu
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2020
• Subjects: Ductile fracture; Fully grouted; Offshore structure; Pushover analysis; Tubular joint; Ultimate resistance; Fully grouted; Ultimate resistance; Ductile fracture; Tubular joint; Offshore structure; Pushover analysis
• ISSN: 0263-8231; 1879-3223
• DOI: 10.1016/j.tws.2020.106761

The nonlinear behaviour of fully grouted (FG) circular hollow section (CHS) X joints and the associated representation for overall frame analysis are investigated in this study. Infilled grout always causes brace buckling of FG X joints under brace compression and leads to punching shear failure of the FG X joints under brace tension. The former is considered as a rigid-joint connection, and only the latter is covered in the current research scope. Joint representation includes the load–deformation formulation and ultimate-strength equation. The load–deformation formulation is developed as a linear function in the elastic stage and a parabolic function in the nonlinear plastic stage. The ultimate-strength equation is based on the fracture study of a series of FG X joints with a broad range of geometric sizes. The fracture study develops a fracture locus of steel S355 and incorporates the fracture locus into the Johnson–Cook model for fracture simulation. A simple ultimate-strength equation is derived based on a straightforward relationship discovered between the nondimensional ultimate resistance and geometric parameters β and γ. The available test data successfully validate both the load–deformation formulation and ultimate-strength equation. •Develop an accurate load-deformation formulation for FG X joints.•Establish the relationship between the equivalent strain-to-fracture and stress triaxiality ratio for steel S355.•Propose a simple equation to predict the ultimate strength of FG X joints under brace axial tension.