Damage criterion and safety assessment approach to tubular joints

Based on the Continuum Damage Mechanics (CDM), a damage criterion is proposed to predict the macrocrack initiation for tubular joints. The guidance on prediction to ultimate load carrying capacity of flawed tubular joints is provided by means of the modified Central Electricity Generating Board (CEGB) Failure Assessment Diagram (FAD). Non-linear FE analyses were carried out on uncracked and cracked T, K and KK tubular joints. Triaxial stress distributions and equivalent plastic strains near weld toes in the chord around the brace were numerically obtained for uncracked tubular joints. The crack driving force, J-integral, and ultimate collapse loads of cracked tubular joints subjected to axial brace loading were evaluated by FE analyses. Load–displacement curves and ultimate strengths for uncracked and cracked T, K and KK-joints were numerically determined. A uni-planar KK tubular joint specimen was tested under anti-symmetrical axial loads. During the test, the load–displacement curve and the ultimate strength were measured. Meanwhile, crack initiation and growth were observed until complete failure. FE and test results show that the damage criterion gives good prediction for macrocrack initiation in tubular joints, and the modified CEGB approach is suitable for the safety assessment to flawed tubular joints.