The optimal control problem is presented either as a regulator problem or as a tracking problem. If feedback control strategy is desired, the regulator problem provides a closed-loop control and the tracking problem provides a combination of closed-loop and open-loop control. Both problems have been applied to the optimal control of a civil engineering structure. It has been shown that if the disturbance is known a priori, then the tracking problem is the most suitable design method and provides the best control response but on the account of an increased cost. On the other hand, the control law provided by the regulator problem does not depend on the type of the disturbance and since it is a closed-loop type, it is considered a suitable means of controlling against uncertain and unexpected disturbances, because it provides the active stiffness and active damping needed to control the structure properly.