This research focuses on deterioration behaviors of the unloading stiffness obtained from loading tests of beam-to-column joints of composite beams and steel beams, and discusses the applicability of numerical analyses. The Ibarra-Medina-Krawinkler model expresses degradations of the stiffness and load capacity based on the hysteresis energy. By giving appropriate parameters, a stiffness deterioration behavior at the positive bending of the experiment was efficiently represented. The difference in hysteresis energy due to the presence or absence of stiffness deterioration reached about 20 % when the value positive bending stiffness dropped to about 80 %.
