Unveiling Longitudinal Failure Mechanisms and Macro Constitutive Modeling of Seat‐Type Bridge Abutments: Lessons From the 2021 M7.4 Maduo Earthquake

ABSTRACT The 2021 Magnitude 7.4 Maduo earthquake resulted in complete damage to typical seat‐type abutments and severe collapse of girders along the longitudinal direction of Yematan Bridge, a representative multi‐span, multi‐frame girder bridge. To address an urgent need for unveiling abutment failure mechanisms, this study performs comprehensive field investigations coupled with in‐depth numerical analyses. Moreover, as an important boundary component for full bridge collapse analyses, a practical macro constitutive model of abutment is eagerly required for computational efficiency. To this end, this study introduces a refined abutment modeling and an associated adaptive quasi‐static pushover analysis approach, which features three innovations: (1) a coupled flexural‐shear model of the backwall to identify failure modes (flexural, flexural‐shear, or shear); (2) distributed p‐y springs, modified from traditional API p‐y springs, to simulate backfill‐abutment interactions; and (3) an adaptive pushover load pattern to capture variations of girder‐backwall contact points. Accordingly, elastoplastic damage mechanisms, critical load paths, and abutment component‐wise resistance contributions against longitudinal seismic loading exerted by adjacent girders are systematically uncovered. Numerical results confirm a predominant flexural‐shear failure mechanism of the backwall and verify the integrity of the pile foundations, aligning closely with the observed earthquake‐induced damage. The originality and strength of the macro constitutive modeling lie in its ability to succinctly encapsulate complex nonlinear girder‐abutment‐backfill interactions into an efficient, transferable, and practical model, advancing seismic collapse analysis capabilities of full bridge‐abutment systems.