Failure assessment of cracked square hollow section T-joints

Three full-scale static strength tests were carried out on pre-cracked square hollow section (SHS) T-joints. In accordance with the experimental results, an accurate crack model for welded SHS joints is proposed in this paper. Based on this numerical model, the load–displacement curves and the stress intensity factors (SIFs) along the crack front are calculated. It is found that the SIF varies greatly along the crack front, and the highest value is located at the brace corner. From Charpy V-notch impact test results, anisotropic fracture toughness was found, and influenced the failure behavior of the damaged joints. Ductile tearing was found to initiate from the crack front parallel to the chord side wall where the fracture toughness was smaller, and not from the crack front at the corner where the SIF value was the highest. Using the plastic collapse load obtained via the twice elastic compliance technique and the fracture toughness obtained from the Crack tip opening displacement (CTOD) tests, the BS7910 Level 2A Failure Assessment Diagrams (FAD) for the three cracked joints are plotted. It is confirmed that the standard BS7910 Level 2A curve gives a conservative assessment for cracked SHS T-joints under brace end axial loads.