In this study a new simple approach for seismic vibration control of three dimensional structures is proposed. This simple approach is based on modifying the stiffness and damping parameters of the structure. The additional stiffness and damping parameters are obtained by solving the Riccati equation in closed loop Classical Optimal Control (CLOC) and with the help of the optimal control gain matrix. Since it is not possible to add the exact optimal damping and stiffness parameters to the structure in practice some representative simple methods to obtain the suboptimal passive damping and stiffness parameters from the optimal control gain matrix are proposed(). Proposed method is applied to a 3-dimensional tier building structure. For this study, a 3-story steel building designed for the SAC project Los Angeles, California region is considered(). The structure is tested under two unidirectional real earthquake excitations. Two active control cases are considered for comparison. In the first case a single active tendon controller is implemented to each story in the north-south direction of the structure. In the second case active tendon controllers are implemented to the structure in both north-south and east-west directions. The results demonstrate that without applying active control forces to the structure, modifying the stiffness and damping parameters can supress the earthquake induced vibrations into the limits desired and the responses are similar to the actively controlled structures under CLOC.