Abstract
This paper discusses the motion characteristics of building structures with soft stories integrated, from the wave propagation point of view. Even in dealing with a normal lumped mass system, if considering the energy transfer from a lumped mass to its next lumped mass, a very clear view can be given to the understanding of the mechanism for the vibration phenomena for these structures. In particular, the paper focuses on why a significantly large deformation occurs at the soft story in these structures. In addition, the relationship between the peak seismic deformation and energy flows in the structures subjected to large-period seismic excitation is quantitatively discussed from the standpoint of energy transfer induced by the wave propagation through the structures.