Floating debris impact on historical masonry arch bridges: Model updating and fluid-structure interaction simulation

Historical masonry arch bridges represent critical transportation infrastructure and irreplaceable cultural heritage, yet they face severe threats from floating debris impact during extreme hydrological events. Existing research primarily focuses on ship impact on modern bridges, paying insufficient attention to the material degradation caused by long-term weathering and water erosion. Moreover, current simulation methods often lack adequate bidirectional fluid-structure interaction (FSI) simulation for woody debris impact, leading to inaccurate safety evaluations. This study takes the Nanjing Putang Bridge—a nine-span historical masonry arch bridge constructed in 1512 and a Chinese key national cultural heritage site—as a case study. Two key contributions are presented: first, the development of a two-stage finite element model updating approach based on operational modal analysis to map material degradation; and second, the integration of the updated model with bidirectional FSI simulation to systematically investigate the bridge’s mechanical response under woody debris impact. Results show that under combined water flow and debris impact, tensile stress concentrates on the side wall of Pier No. 5 and joints between Arch No. 3 to No. 6 and their respective arch shoulder walls, without causing structural collapse. Additionally, existing ship collision codes overestimate the impact force of floating woody debris, while the current simulation impact values are only 13–41 % of code-derived ones. This overestimation is corrected by introducing a regression-derived dynamic correction coefficient. This study provides a reliable numerical framework for the safety assessment of historical masonry arch bridges against floating debris impact. • A method incorporating two-stage model updating and bidirectional FSI is proposed. • A fully flow-driven impact process of floating woody debris is reproduced. • The impact mechanism influenced by flow conditions and debris attitude is revealed. • The response of historical bridges to floating woody debris is analyzed. • The dynamic correction coefficient for the specification deviation is derived.