The development in construction technology has led to a trend toward constructing rather flexible structures whose design involves certain problems as safety, human comfort, and increased risk of damage. A solution to these problems consists to a certain extent in the application of structural control by using active or passive control mechanisms. The advantages encountered in using active control mechanisms to control the structures' response have led to various attempts in applying active control theory to civil engineering structures. The implementation of the control force, the choice of the proper type of the control device and its components, and the interaction of some modes of vibrations and its effect on the behavior of the controlled structure are being studied in this paper. A simple span bridge subjected to a deterministic, moving load is taken as an example.