Abstract: To investigate the damage response of steel members and frames subjected to large-strain and low-period cyclic loading, a damage initiation criterion of structural steel is proposed, based on the Bao-Wierzbicki locus of the equivalent plastic strain and stress triaxiality. Then, 10 tensile tests on Q235 structural steel are carried out to determine the damage evolution criterion. The validity of the proposed criterions is proved in the following damage simulation analysis of an H-shaped beam, two steel joints and a frame by using the finite element software ABAQUS. The simulated results show that the finite element analysis curves, considering the damage criterions, compare well with the experimental curves, which proves that the proposed damage criterions could accurately simulate the degraded characteristics of strength and stiffness of steel members and frame due to cyclic loading. It also shows that model considering the damage criterions could accurately predict the failure locations of the structure. The proposed damage criterions provide a powerful tool for damage analysis of steel members and frames subjected to large-strain and low-period cyclic loading.