Concerns over our inability to control and protect civil structures and mechanical equipment during a seismic activity have reached alarming levels as a consequence of the damages inflicted: case and point, as observed when the city of Christchurch was reduced to rubbles by an earthquake in 2011. Earthquakes are natural phenomenon that we do not have control over. The only way to avert catastrophic destruction of structures is by making them earthquake tolerant. Presently, base isolators and tuned mass dampers are the prevalent techniques of achieving such tolerance. Other more sophisticated solutions for reducing the effect of seismic excitation are dynamic absorbers such as tuned mass dampers. The former has however not been considered as a generalizable solution for protecting civil structures and thus the development of new methods for protecting civil structures is needed. Researchers have thus reverted to use of active vibration control whose effectiveness of an active switch of the stiffness of the base in seismic isolation is notable.
Marco Barbieri and Francesco Pellicano at the University of Modena and Reggio Emilia in Italy in collaboration with Sinniah Ilanko at The University of Waikato in New Zealand investigated the active stiffness control of a system under seismic excitation. Their goal was to comprehend whether a stiffness foundation control is capable of reducing the effects of a base excitation. They also hoped to estimate the characteristics required for developing a real control system for future experimentations. Their work is published in the journal, Nonlinear Dyn.
The research technique conducted involved the adoption of a simple two-degrees of freedom model comprising of two masses: one to represent the base of the modeled two-storey building and the other to act as a suspended mass connected to the base by a spring. Next, the researchers employed a control strategy involving only few parameters. They then proceeded to employ the control strategy to a measured earthquake signal.
The authors observed that for the simulated cases, the external forcing frequency matched the fundamental frequency of the system. The team also noted that the applied control strategy was able to reduce the maximum acceleration of the suspended mass by 88%. Additionally, they recorded that the passive seismic isolators were effective in filtering horizontal vibrations.
The study has successfully presented the theoretical cross-examination of a novel control technique for seismic isolation of buildings/equipment. This parametric study on a test problem has shown that the best control for all the forcing frequencies can be obtained for a base stiffness reduction of one half. Moreover, it has been seen that the proposed method reduces the maximum acceleration of the top mass by 55% without introducing larger vibrations at the base; the effectiveness of the control strategy is proven by maximum value of the total energy of the system, which is reduced by 81%. Altogether, the results obtained here indicate that the stiffness control strategy proposed is an efficient filter for vertical seismic vibration isolation.
Marco Barbieri, Sinniah Ilanko, Francesco Pellicano. Active vibration control of seismic excitation. Nonlinear Dynamics July 2018, Volume 93, Issue 1, pp 41–52Go To Nonlinear Dynamics