Fishbone-shaped frame is approximate model for seismic analysis of multibay multistory planar frame. However, the previous formulation of modeling is unable to consider strength deterioration in a large plastic deformation range. This paper proposes the method of modeling of multibay multistory planar frame considering strength deterioration for the purpose of investigating complete collapsing behavior. Seismic response analyses of 4- and 8-story steel moment frames are conducted. The numerical analyses show that the modeled frame can predict the state of plastic hinge and seismic energy absorbed by complete collapse.