PID Controlled Semi-Active Device for FPS Isolated Structure

The friction pendulum system (FPS) is a popular base isolation device to minimize seismic forces transferred to the structures. Constant isolator frequency of FPS may produce the resonance problem in the isolated structure for near-fault earthquake ground motions. So FPS may have limited effectiveness in isolating structures subjected to certain types of seismic activity. For improving the performance of such structures, a control system may be very useful to obtain the desired results. To address this issue, a PID controlled semi-active device is proposed in this study. PID algorithm is widely used in the industries and compared to other controllers, PID is simple and has a clear physical meaning. The structural model and the isolator properties considered for the isolated structure are developed as state-space matrices and are converted into transfer functions. Using BODE approximations, second-order plus dead time (SOPDT) models for these higher order transfer functions are derived to attain PID parameters. The PID parameters are tuned by means of Routh- Hurwitz technique. The usefulness of the proposed technique is established through numerical simulations for FPS isolated structures with two degrees of freedom. Results of the investigations indicate that a PID controller reduces shear at the base and sliding displacement of the structure isolated with FPS simultaneously. Furthermore, the resonance problem of FPS isolated structure can be nullified using the proposed technique.