Effect of Seismic Isolation System on Seismic Behavior of Irregular Continuous-Girder Bridges Considering SSI

The varying pier heights in long-span multi-span continuous-girder bridges create substructures with uneven stiffness distribution, which leads to non-uniform distribution of massive superstructure inertial forces among substructures. This paper investigates the internal force homogenization mechanism of seismic isolation systems in irregular long-span continuous bridges and quantitatively evaluates the homogenization effectiveness. Taking the irregular continuous-girder bridges in China’s Hong Kong-Zhuhai-Macao Sea Crossing Project as engineering prototypes, finite element modeling incorporates soil-structure interaction (SSI) effects. Five distinct pier height parameters are considered to characterize height disparities. The isolation system is implemented using lead-rubber bearings, with nonlinear dynamic analyses conducted under five sets of bidirectional seismic excitations. Curvature ductility coefficients serve as damage indices to quantify the seismic performance of irregular continuous bridges with and without isolation systems under intense ground motions. Results demonstrate that the pier-bottom horizontally aligned configuration exhibits comparable shear response characteristics and torsional effects to the pier-top horizontally aligned configuration, rendering it recommended for shake table investigations of irregular bridge systems. The seismic isolation system effectively balances internal force imbalances induced by pier height discrepancies through flexible coordination mechanisms, concurrently mitigating asymmetric deformation and torsional instability risks, thereby enhancing global structural synergy. Under SSI conditions, the isolation layer demonstrates universal damping efficacy across diverse foundation conditions, with both isolated irregular and regular bridges maintaining intact pier columns under strong seismic excitations.