Risk-based probabilistic assessment of a bridge collapse due to abutments scour. A case study

Many bridges are constructed over waterways, exposing their support systems to scour caused by flowing water-induced bed shear stresses over time. This study focuses on analysing the local scour beneath an abutment, which led to the collapse of a poorly reinforced concrete bridge in Italy. The analysis investigates the causes of the collapse on the basis of a geotechnical characterisation of the subsoil foundation and mechanics characterisation of the abutment. By estimating the scour amplitude below the abutment, an advanced Finite Element fracture mechanics model was used to study the collapse of the bridge. The study makes it possible to assess the probability of collapse based on the scour width beneath the abutment and offer an approach to assess the safety of infrastructure. Finally, the results show that the empirical model for shear capacity is overly unconservative and sometimes unreliable in this special context. and therefore failure should be predicted from the fracture mechanics based on adopting appropriate reduction factors for shear capacity.