Nonlinear Static Pushover and Eigenvalue Modal Analyses of Quasi-Isolated Highway Bridges with Seat-Type Abutments

In recent years, bridge engineers in Illinois developed an innovative “quasi-isolation” design strategy to improve bridge seismic resilience in geographical regions with low-to-moderate seismicity, such as the Midwestern United States. Different from conventionally isolated bridges, non-seismically designed bearing components are employed as sacrificial fuses between the superstructures and substructures of quasi-isolated bridges. These fuses and conservatively designed seat width at substructures are employed to protect the bridges from excessive damage and collapse during major earthquakes. Pushover analysis results are used in this study to provide insight into bridge lateral response characteristics. They are also used to evaluate fusing performance of sacrificial connections and adequacy of bearing seat width, as well as to estimate potential damage to bridge substructures. Additionally, modal response characteristics obtained from eigenvalue analyses performed in elastic and inelastic bridge deformation states imply that a nonlinear single-degree-of-freedom system considering strength and stiffness degradation may be able to capture the dynamic response of typical quasi-isolated bridges.