Based on the Continuum Damage Mechanics (CDM), a damage criterion is proposed to predict the macrocrack initiation for tubular joints. Nonlinear FE analyses on T, K and KK tubular joints were performed by using the ABAQUS package. Load-displacement curves and ultimate capacities for these joints were numerically determined. Triaxial stress distributions and equivalent plastic strains near weld toes in the chord around the brace were obtained from FE results. 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 results show that the damage criterion gives good prediction for macrocrack initiation of tubular joints; Analytical, numerical and experimental results for the ultimate strengths of tubular joints are consistent.
During the recent Kobe Earthquake, many steel structures were damaged owing to the initiation and growth of cracks. Ductile macrocracks often initiated at weld toes (Wang et al 1996, Makino et al 1995) after structures sustain excessive plastic strain. These cracks frequently led to a premature failure of structures. The previous T, K and KK-joint test results gave a conclusion that cracking in the chord wall is one of the important failure modes. The cracks often occurred along the weld toes between the tension brace and the chord and propagated through the chord wall to failure. In previous work (Makino et al, 1995), a crack was assumed to have formed when the tensile plastic strain reached a value corresponding to the ultimate tensile strength of material. However, This method to determine crack initiation is not very reliable without experimental verification, because crack initiation is not only dependent on the tensile plastic strain but also on other parameters
