The feasibility of applying active control theory to control both the transient and steady state response of a two cable-stayed bridge has been investigated. The bridge has been modeled as a two degree freedom system in bending and torsion, excited by both buffeting and self-excited loads. The existing suspension cables have been used as active tendons by which the control forces are applied to the bridge deck at the points of the anchorage. The control force from each suspension cable is actuated through a hydraulic-servomechanism which is regulated by the sensed motion of the bridge deck at the anchorage of the cable. Stability and steady state response analyses have been presented for both controlled and uncontrolled motion. The power requirement for the control devices has been derived. Finally, numerical examples have been worked out to demonstrate the feasibility of the derived theory for two cable-stayed bridges. / Ph. D.