A methodology for the rapid and reliable assessment of existing masonry arch bridges containing defects

Masonry arch bridges remain a vital part of the road and rail infrastructure. Many of those structures have already been in service for hundreds of years and are currently showing signs of defects due to material deterioration and structural damage. This paper aims to propose a methodology to evaluate the load-bearing capacity of in-service masonry arch bridges, taking into account their existing defects. According to the method, first, defects observed in masonry arch bridges during visual inspection are categorised based on their severity level in accordance with the Italian Railway Instructions. Subsequently, the defects are incorporated into an in-house two-dimensional rigid-block limit analysis code to evaluate the load-bearing capacity of single span masonry bridges with spans ranging from 6 to 20 m. The representation of defects including the loss of bricks, loss of mortar, surface spalling were taken into consideration using a probabilistic approach through the Monte Carlo method. From the results analysis, it was shown that for bridges containing same level of defect, the loss of bearing capacity (calculated as the collapse multiplier of the damaged bridge over the collapse multiplier of the undamaged bridge) is greater for bridges with shorter spans compared to those with longer spans. Also, loss of bricks from the arch ring leads to more significant reductions in the bridge’s load-bearing capacity compared to loss of mortar joint and surface spalling. Finally, the simultaneous presence of multiple defects leads to greater losses in load-bearing capacity and variations in the collapse mechanisms of the bridge. This study offers a simplified approach for quantitatively assessing the reduction in load-bearing capacity of masonry bridges containing defects, providing valuable insights for the effective management of existing masonry bridge stock. • A methodology for the rapid assessment of existing masonry bridge. • Defects are incorporated into a two-dimensional rigid-block limit analysis code. • Considered defects including the loss of bricks, loss of mortar, surface spalling. • Assessing the reduction in load-bearing capacity of masonry bridges containing defects.