Base versus top active control to improve dynamic and seismic performances of rigid blocks

This paper compares the efficiency of two active control systems based on the same control algorithm in protecting rigid block-like structures from overturning. The control algorithm is the Pole Placement Method that is aimed at transforming the rest position of a rigid block into a stable equilibrium point. The two control systems differ in the position of the actuator driven by the active control algorithm. In the first case, the block is placed on a horizontally translating support that is connected to the ground by an actuator able to provide a controlled displacement. In the second case, a small mass able to run at the top of the block is driven by an actuator capable of applying a controlled displacement. This kind of protection system is commonly called Active Mass Damper. The effectiveness of the two control systems is analysed by comparing the overturning spectra that represent the amplitude of the harmonic excitation able to overturn the block versus its circular frequency. Several simulations have been conducted using different recorded earthquakes to evaluate the performances of the two control methods in the reduction of the rocking angle and the protection from the overturning of the block. The results show the excellent performance of both the considered control systems.