The modified CEGB approach is applied for the evaluation of structural integrity for defected tubular joints. The guidance on prediction of ultimate load carrying capacity of flawed tubular joints is provided by means of the modified CEGB FAD. Cracked T, K, KK tubular joints were analyzed by nonlinear FE method. The crack driving force, J-integral, and ultimate collapse loads of cracked tubular joints subjected to axial brace loading were evaluated by FE analyses. From these results, two assessment parameters were available to construct the FADs for cracked tubular joints. The results show that the modified CEGB approach is suitable for the safety assessment to flawed tubular joints. Load-displacement curves and ultimate strengths for untracked and cracked T, K and KK-joints were also obtained by FEM. Compared with test values, FE results show to be reasonable with regard to the effect of cracks.
Recently, the crack failure has been gradually realized as one of the principal causes of damage to steel structures. Ductile cracks often initiated at weld toes in tubular structures (Wang et al, 1996, Makino et al, 1995) after structures sustain excessive plastic strain. These cracks frequently led to a premature failure of structures. Therefore, it is essential to understand crack growth behaviour and to be able to assess the significance of defects in steel structures. In elastic-plastic fracture mechanics, the J-integral has been proved to be a useful parameter to control the crack initiation and a small scale propagation for ductile materials. The fracture assessment procedures introduced by the CEGB (Harrison et al, 1976; Kumar et al, 1981) are based on the Failure Assessment Diagram (FAD) approach including the J-integral. Milne (1983) then developed this method into a new modified R6 approach based on the ratio of engineering ultimate strength divided by engineering yield strength.
