Performance and robustness assessment of roadway masonry arch bridges to scour-induced damage using multiple traffic load models

Masonry arch bridges are highly vulnerable to floods and particularly to scour, as demonstrated by the many collapses that regularly occur in Europe. Scour levels that do not directly cause the collapse of a bridge may result in a significant reduction of their capability to withstand traffic loading. Thus, research on the performance of masonry arch bridges under combined scour and traffic loading, and their structural robustness, is of paramount importance. This study evaluates the behaviour of masonry arch bridges subjected to scour and traffic loading by analysing a representative case study with a three-dimensional finite element model developed in Abaqus according to a macro-modelling approach. Traffic load is selected in accordance with different code-based models, including those provided by Italian guidelines for safety assessment of existing bridges. The scouring process is imposed through the progressive removal of elements at the foundation level. Displacements and internal stress distributions for different bridge components are recorded and the capacity of the masonry bridge is estimated under increasing traffic load for different scour levels. Results are obtained in terms of both local and global response parameters to provide useful information on threshold levels for bridge safety and monitoring. The sensitivity of the bridge structural performance to material properties and traffic load position is also assessed. The study results can be useful to inform the decisions to be taken by bridge stakeholders (e.g. close bridge, limit traffic, keep bridge open) based on scour and/or structural response measurements.