Adaptive control strategies for active mass driver system with physical limitations

Active Mass Dampers are mainly employed for the reduction of wind-induced vibrations in high-rise buildings, in order to meet appropriate comfort criteria. When such active devices are subjected to seismic events, they can experience large amplitude vibrations and exceed stroke limits. This can reduce the performance of the control system or even produce damages to the control device as well as to the structural system. In this paper, a non-linear control strategy is proposed for handling stroke limits of an Active Mass Driver system. The control force is given by the sum of a linear function of the state of the system and a dissipative force that becomes effective close to the physical limit of the actuator. The skyhook strategy is adopted for the linear term while the variable gain term is moduled by a nonlinear coefficient dependent on the relative displacement of the AMD. Experimental and numerical free vibration tests are carried out on a scaled-down five-story frame structure equipped with an AMD. The proposed non linear control law proved to be effective in reducing the structural response and avoiding the stroke limit crossing, at the expense of a small increase of structural displacements and a slight increase of structural accelerations.