Limit State and Discontinuum-Based Structural Analyses of the Pakenham Bridge (Ontario, Canada)

Stone and brickwork masonry arch bridges constitute historic landmarks and are an integral part of the road and railway transportation systems in Canada. However, the accurate prediction of their structural behavior and load-carrying capacity is a challenging task, given the complexity of the material behavior, geometrical features, and the soil-structure interaction phenomenon taking place between the masonry and soil backfill. Typically, continuum-based approaches (e.g., standard finite element analysis) may fail to simulate the influence of the morphological features of masonry systems and the discontinuous nature of the material. This research aims to provide an in-depth understanding about the computational modeling of masonry arch bridges by adopting more suitable structural analysis approaches, namely, limit state and mixed discrete-continuum analyses. The latter enables a detailed representation of the structural components in a masonry arch bridge, including soil backfill, arch barrel, and spandrel walls, in a 3D setting based on the discrete element method (DEM). In contrast, limit state analysis adopts rigid blocks with active/passive soil pressure applied on the extrados of the arch barrels. Both numerical modeling techniques are adopted to simulate one of Canada’s oldest multi-span stone masonry arch bridges, the Pakenham Bridge (Lanark County, ON, Canada). In the mixed discrete-continuum approach, a progressive procedure is followed where the level of complexity in the computational model is gradually enhanced. First, the arch skeleton is analyzed, and then the effect of soil backfill is captured by adding a continuous medium within the framework of the DEM. Finally, the spandrels walls are included to examine their out-of-plane deformation under the serviceability and ultimate state conditions. The results indicate the differences between 2 and 3D analyses and highlight the influence of soil backfill on the load-carrying capacity of arch bridges. Furthermore, important inferences are made regarding the modeling techniques and the macro behavior of the analyzed multi-span stone masonry arch bridge.