An effective fixed-base model with classical normal modes for soil-structure interaction systems

To simplify the analysis of soil-structure interaction systems, various fix ed-base models have recently been proposed by the author to efficiently rep resent the SSI system and have been shown to have good accuracy. However, t he modified mass and damping matrices of these models do not hold the prope rties of symmetry and orthogonality. Difficulties may consequently be induc ed for these models in applying conventional computer codes to carry out dy namic analysis. In the present paper, this problem is further explored to e stablish a fixed-base model possessing classical normal modes. Formulated i n the modal space, this fixed-base model is constructed through applying an iteration algorithm to incorporate the Gram-Schmidt orthogonalization proc ess. The convergent real orthogonal mode vectors, natural frequencies, and modal damping ratios are directly determined for this model. It is demonstr ated with a numerical example that this new fixed-base model retains excell ent accuracy. Accordingly, the complicated SSI systems can be directly anal yzed using conventional computer codes for structural dynamics with the fix ed-base model developed in this study. (C) 2001 Elsevier Science Ltd. All r ights reserved.