Chord plastification strength of longitudinal plate-to-CHS joints with steel grade up to 460 MPa under combined axial compression and in-plane bending

Abstract

Up-to-date design rules for tubular joints with welded branch plate(s) were recently formulated in prEN 1993-1-8. The design rules cover joints of high-strength steel tubular members whose yield stress is up to 460 MPa by incorporating the material factor (or joint strength reduction factor). However, the background data for the specified material factor need to be further augmented. In this study, the material factor for steel grade 460 was further investigated based on an extensive test-validated numerical analysis. Longitudinal X- and T-type plate-to-circular hollow section (CHS) joints were considered in the analysis, and their nondimensional geometric parameters were carefully chosen to induce a ductile chord plastification failure only. For the loading conditions, the combined axial compression and in-plane bending (IPB) were included in addition to the individual loading case. It was first shown that when IPB loading is involved, the use of a widely accepted 3% deformation limit criterion often yields a conservative joint strength rating. A more reasonable criterion is proposed considering both the 3% indentation limit and an additional limit in terms of the joint rotation angle. With the new deformation limit criterion, the code-specified material factor (0.90) for steel grade 460 was found to be appropriate for the X- and T-joints regardless of the loading type. Meanwhile, it was also noted that the current design standards or guides do not provide an interaction relationship for the design of joints under combined axial compression and IPB. Based on the analysis results of this study, the use of a linear interaction equation is recommended for both mild and high-strength steel joints.