B Rajabi - Department of civil engineering, Saghez branch, Islamic Azad University IAU, Saghez, Iran
O Bahar - Assistant Professor, International Institute of Earthquake Engineering and Seismology (IIEES

In active controlling of structures, we can monitor just one or few modes of structure. Applied control force to active control devices which regulated on main vibration mode of structure and it seems that large time delays have deteriorated effects only on the controlled mode. In this paper we evaluate time delay’s effect on the other modes that are not controlled. For this reason, used a 2D 8-shear story that subjected to EW Elcentro ground motion. For processing and determining structure’s responses, discrete instantaneous optimal control method is used. Structure and control system are analyzed in many different time delay and after that found out time delay in active structural control system loop has not only mortal effect on controlled mode but also has similar effects on the other uncontrolled modes. In the other word, time delay has approximately same effects on all vibration modes of structure

Higher vibration modes, Active control, DIOC algorithm, Time delay effect