9703805 Masri Presently used actuators to generate control forces are generally inadequate for limiting the response of civil structures under strong earthquake shaking. There is a critical need for a new generation of actuators that have the capability of adequately performing under strong ground motion which may induce significant nonlinear deformations in structures. The objective of this research is to develop an innovative semi- active damping augmentation device for controlling the seismic response of dispersed civil structures. The control procedure uses nonlinear auxiliary mass dampers with adjustable (adaptive) motion-limiting stops, located at selected positions throughout the structure, to inject an optimum amount of "chaos" in the structures dynamic response by disorganizing the orderly process of amplitude buildup. The degree of the structure's oscillation in the vicinity of each semiactive nonlinear actuator determines the actuator's actively-controlled gap size and activation time. By using control energy to adjust the actuator's critical parameters instead of directly attenuating the motion of the structure (which conventional active control methods do), a significant improvement is achieved in the total amount of energy expended to accomplish a given level of vibration control. A sequence of analytical and experimental studies by means of a bridge model to be provided with several innovative nonlinear actuators and subjected to multiple-support earthquake excitation by seismic shakers will also be conducted. ***
