Semiactive control of nonlinear isolated bridges with time delay

The effectiveness of semiactive control using variable dampers is studied for nonlinear isolated bridges, which exhibit inelastic response at both the columns and the isolators, under near-field ground motions. The linear quadratic regulator optimal control algorithm is used to command variable dampers. Time delay is inevitable in the operation of control systems and may deteriorate the control performance. A time-delay compensation method based on the Newmark's method is proposed to mitigate the degradation of control performance due to time delay. A five-span viaduct with high-damping-rubber isolators is utilized for analysis. The results show that semiactive control with variable dampers is effective in reducing the seismic response and provides the similar performance by linear quadratic regulator active control. The semiactive control also shows similar or better performance than the passive control with the maximum damping coefficient of the variable damper. The proposed Newmark compensation method shows superior compensation performance on the time-delayed nonlinear system under semiactive control.