In order to grasp the dynamic characteristics of structure considering soil structure interaction, the eigenproperty of structure having identical stiffenss and mass distribution is evaluated. As evaluation methods, two approaches are introduced. The first is based on explicitly representing the determinant of dynamic stiffness matrix by the polynomial expression using the property of the cofactor expansion of tridiagonal matrix having common elements. The another method is based on explicit representation of transfer function using the transfer matrix method which is powerful for periodic structures. The dependency of the eigenfrequencies and damping ratios on the analysis model, story and size of structure and stiffness of soil are studied. First, the effect of soil-structure interaction on the eigenfrequencies for undamped models are studied. Secondly, the effect of damping on the eigenproperty is studied through the complex eigenvalues and transfer functions and it is clarified that the soil-structure interaction gives a large influences on the dynamic property of structures, which points out the limitage of conventional real eigenanalysis and the importance of proper selection of damping model.
