Masonry bridges in the Italian railway network: statistical survey and assessment strategy

The evolution of railway traffic tends towards an increase of the carriage loads and asks for more D4-class commercial lines. This urges the need for re-classification of the existing lines to the needed loads. An important part of the work is the assessment of existing masonry bridges which constitute a very important part of the railway system also if the bridge is of ordinary importance. For this reason, the RFI - Italian Railway Network started a wide research project on the assessment procedures for masonry bridges. A recognition of historical sources and of the available archives allowed to sketch the main characteristics of the Italian railway bridge stock and to characterize them from a statistical point of view. A multi-level procedure is developed with the aim of both modelling the effective response of the bridge, in its present state, and foreseeing its response close to the limit conditions and the effectiveness of refurbishment techniques. Simplified approaches and FEM models are formulated in order to give a coherent mechanical modelling of the bridge at different levels of detail, i.e. for the analysis of the global structural response and for deep and detailed information on local effects, respectively. Besides, FEM models allow a first approach to the dynamics of the bridge. Simplified methods for the plane analysis of the bridge and FEM analyses consisting of 3-D linear models under service loads are currently under development and are discussed in this paper. Simplified approaches for the out-of-plane response of the bridge and non linear 3-D FEM models under service conditions and loaded up to the final collapse are to come in the near future. A real in-service bridge is taken as example of the procedure, showing that the different approaches developed at different levels can be used to get a first glance of the structural behaviour of the bridge.