The effectiveness of seismic displacement response control for isolated bridges, which behave nonlinearly at both the columns and the isolators, is studied using the LQR optimal active control. A typical viaduct is analyzed for evaluation. An extensive parametric study of weighting matrices is carried out to examine the effect on reducing the displacement response. The results indicate that the active control is effective in reducing the deck displacement at small control force levels. Further,

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... the effectiveness of saturation of control force is investigated for preventing excessive control at large control force levels. Finally, the active control is compared with the passive control using viscous dampers.