Rocking responses of spread foundations may occur during extreme earthquakes. Rocking responses result in the isolation effect on the bridges. When a bridge is designed using isolators and spread foundations, double isolation effects may further decrease the seismic-induced forces under extreme earthquakes. However, the deck displacement becomes excessively large when subjected to a near-field ground motion. Thus, passive viscous dampers are applied to the bridge for decreasing the displacement responses in this study. Compared with typical isolated bridges, the irregular isolated bridge has different stiffness at each column and abutment. The particle swarm optimization-simulated annealing (PSO-SA) hybrid searching algorithm is employed to find the optimum damping coefficients and the locations of viscous dampers.