Xiaowei Wang

Two neighboring highway girder bridges exhibited significantly different damage during the 2021 Magnitude 7.4 Maduo earthquake. Yematan Bridge, a multi‐frame girder bridge (five frames each with five spans, denoted as 5 × 5 spans), suffered collapse of 70% of the total number of girders (mostly on the north side), expansion joint damage from girder‐to‐girder pounding, and severe north abutment damage due to girder‐to‐abutment pounding, whereas the single‐frame Heihe Middle Bridge with three spans (1 × 3 spans) remained almost intact. This contrast highlights the crucial roles of frame/span numbers and girder‐to‐girder/abutment pounding in bridge performance. In this regard, a comprehensive parametric analysis using finite element full bridge models is conducted to reproduce the observed damage and to explore pounding and collapse mechanisms, considering the effects of near‐fault pulse‐like ground motions (i.e., pulse period, velocity, and wave passage) as well as the frame/span numbers. A novel pounding Gantt plot is proposed to visualize the successive pounding events from girder‐to‐girder to girder‐to‐abutment, called chain pounding in this study. Results show that significant chain pounding occurs in Yematan Bridge under specific long‐period pulse‐like motions with wave‐passage effect, which is the primary cause of the severe north abutment damage and girder collapses. In contrast, such a devastating chain pounding is absent in the single‐frame Heihe Middle Bridge, where stronger abutment constraint effects on girders shift its vibration period away from unfavorable pulse periods of ground motions, thereby mitigating damage. Furthermore, decreasing the frame/span numbers reduces bearing displacements under long‐period pulse‐like ground motions, but increases them under short‐period motions. Thus, seismic design of multi‐frame and multi‐span highway bridges at near‐fault sites should carefully consider relationships between bridge length and pulse period of ground motions.

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.