Plastic collapse load prediction and failure assessment diagram analysis of cracked circular hollow section T-joint and Y-joint

ABSTRACT This paper concerns the validation of standard safety assessment procedure given in BS 7910 for cracked circular hollow section T‐joint and Y‐joint, using the finite element (FE) results. A robust and efficient FE mesh generator is developed to produce the 3D models of the cracked joints and to calculate the elastic J‐integral (Je) and elastic–plastic J‐integral (Jep) values of the crack respectively. In order to verify its accuracy and convergence, the plastic collapse loads (Pc) obtained from experimental tests and FE predictions are compared; they agree very well with each other. It is also found from experimental tests that the plastic collapse loads (Pc) predicted using the BS 7910 reduction factor (FAR) are safe and conservative. Subsequently, the failure assessment diagrams (FADs) of five cracked T‐joints and three cracked Y‐joints are constructed using the FE results, following the J‐integral method, which is classified as Level 3C in BS 7910. Thereafter, a comparison between the constructed FAD curves and the standard Level 2A curve is carried out, and it is observed that the safety assessment results using the standard Level 2A curve might be unsafe because some parts of the constructed FAD curves fall inside of the standard one. A penalty factor of 1.15 working on both the elastic–plastic J‐integral and plastic collapse load (Pc) is proposed to move all the constructed FAD curves just outside of the standard Level 2A curve.