An Idealized Structural Unit is developed for predicting the elastoplastic behavior of tubular members with crack damage under combined tension and bending. This method can be easily applied to the elastoplastic analysis of frame structures containing through-thickness cracks. Ductile crack growth is considered using CTOD and CTOA as fracture parameters which rule the initiation and continuation of the crack growth, respectively. The tangential stiffness matrix of a cracked member before reaching the ultimate strength of the cracked section is evaluated by introducing the crack spring element having the compliance of cracked section into the node of beam-column elements. The stiffness formulation after the ultimate strength of the cracked section is based on the plastic node method. The elasto-perfectly plastic material is assumed and the values of CTOD and CTOA are evaluated based on the Sanders' semi-membrane shell theory. The results are compared with those of the finite elemet shell analysis, and the rationality and effectiveness of the proposed method are demonstrated.