Multi-objective optimization of nonlinear passive control systems for seismic response mitigation of bridges

A substantial number of existing bridges in high-seismicity countries like Italy were not designed for seismic actions, thus being particularly vulnerable to earthquake-induced motions. While deck isolation from piers is commonly employed to reduce base shear and seismic vibrations, it often fails to keep deck displacements within acceptable limits, thus preventing a large-scale application of this technology. Damping levels higher than those provided by common isolation devices require nonlinear analysis methods, including unconventional hysteresis models. Aiming at improving the seismic response of bridges, this study proposes a unified optimal design strategy for bridges adopting generalized non-linear rate-dependent (RD) and rate-independent (RI) control systems based on Seleemah–Constantinou and Vaiana–Rosati models, respectively. The resulting generalized nonlinear control systems are then optimized using a meta-heuristic algorithm by simultaneously considering multiple competing objectives to mitigate bridge deck displacement, acceleration, and transmitted force to the pier. The RD and RI control systems tend to yield a displacement-constrained and an acceleration-constrained design objective, respectively. In both cases, the optimal Pareto front shows a significant improvement over the base-isolated response in terms of isolator displacement with further reduction or minimal increase in the force transmitted to the pier. The results of this study contribute to the development of an effective seismic mitigation strategy for bridges where both base shear and deck displacement provide major constraints.