STRUCTURAL ASSESSMENT OF DAMAGED MASONRY ARCH BRIDGES: A PARAMETRIC STUDY BASED ON LIMIT ANALYSIS

Many Italian and worldwide in-service infrastructures were realised in the first half of the last century based on traditional techniques and empirical criteria. In this regard, masonry arch road bridges deserve particular attention given their ancientness, as well as the fact that they are often characterised by lack of maintenance and structural upgrading interventions. Furthermore, recent large-scale surveys have highlighted frequent damage due to anthropic (i.e. traffic) and natural (i.e. earthquakes, soil settlements, degradation, etc.) actions, which may inevitably affect their structural capacity. Given the strategic role bridges play in the road network, the structural protection of masonry arch bridges is a challenge that must be faced with vigour and determination. The knowledge of the structural behaviour of such structures subjected to loads of different natures is necessary to implement effective structural improvement interventions and cannot discern from the damaged configurations. The problem is as complex as it is wide, also considering that its generalisation is quite difficult given the vast variety of existing masonry arch bridges, as a result of merging different technologies, materials and geometries also according to the territory where the structures were built. Starting from this premise, the present paper proposes a possible approach to the problem of capacity evaluation of damaged bridges based on limit analysis to determine collapse multipliers in different conditions. In particular, the study focuses on the family of diminished or three-centered arches and a preliminary geometrical characterisation is thus carried out. The study provides a parametric analysis performed with a routine specifically developed, of a bidimensional arch subjected to horizontal load. The collapse multiplier was evaluated both for the undamaged condition and considering possible damage to the intrados. The latter was modelled with a local reduction in thickness whose position was varied along the entire intrados of the arch. The study therefore provides an evaluation of the position of the intradossal damage which leads to the greatest loss of capacity for each of the geometries considered.