F. Amini - Assoc. Profesor, Civil Eng. Dept., IUST, Tehran, Iran
F. Danesh - Ph.D. Student, Civil Eng. Dept., IUST, Tehran, Iran

In the last two decades active variable stiffness method has been successfully used to control the structures. In recent years semi-active control method has mostly been studied because of its low cost and reliability.The main objective of this study is to obtain required practical stiffness for any selected short period of time to control the behavior of structure so that displacements and accelerations do not exceed the allowable values. The semi-active system proposed herein is based on the orderly iteration of changing stiffness of structures. On the other hand it is assumed that the number of bracings which can be active automatically is limited. The feasibility of the method is shown by the eight and ten storey frame structures.