An automatic discrete macro-element method based procedure for the structural assessment of railway masonry arch bridges

Railway masonry arch bridges belong to our cultural heritage structures that have to be safeguarded and still represent a high percentage of the railway infrastructures of many countries, particularly in Europe. These structures are difficult to characterise in terms of real structural geometry and material mechanical characteristics and in many cases have been subjected to structural retrofitting or modifications that are not sufficiently documented. The continuous upgrading of the railway network implies the need to provide a structural assessment of each existing masonry bridge under static and dynamic loading conditions. A reliable structural assessment of old masonry arch bridges is, however, a very complex task. Spatial geometric consistency, assignment of proper mechanical properties and the need to consider several load combinations, associated to all possible positions of train loading, are important requirements for performing a reliable numerical model. The use of ‘General purpose’ three-dimensional nonlinear Finite Element (FEM) software, although accurate, is extremely time consuming in terms of model implementation and computational effort and requires expert judgement. In this paper a Discrete Macro-Element Method (DMEM) approach, previously applied to model the behaviour of different masonry structural typologies, is applied for the structural assessment of a masonry bridge. The computational cost of the proposed numerical approach is greatly reduced in comparison to that involved in nonlinear FEM simulations or Discrete Element Method (DEM) strategies based on a meso-scale discretisation. The discrete DMEM approach is applied for the structural assessment of a particular masonry arch bridge characterised by larger central span about twice the size of the other identical arches. The results show how the proposed DMEM can be successfully used for performing the structural assessment of masonry bridge with a reduced computational burden, compared to the nonlinear finite element simulations, and an easy and straightforward interpretation of the numerical results.