Structural analysis of a multi-span railway masonry bridge combining in situ observations, laboratory tests and damage modelling

The paper presents a structural analysis by means of an orthotropic damage model of a multi-span masonry railway bridge built in the early years of the 20th century. Its aim is to show how this type of model allows for the current bridge mechanical behaviour under service loads to be assessed and the ultimate load to be forecast. It includes a phase of research on archived documents, an in situ investigation phase, an experimental phase carried out on core samples in the laboratory, and a computation phase. Among the different calculation steps, a simulation of the bridge history is performed in order to consider the current cracked state induced by support settlement. In a following step, the traffic loads are applied to assess the mechanical behaviour of the bridge under service loads up to failure. The mechanical behaviour of masonry is described by means of an original 3D anisotropic damage model able to consider the opening and the progressive reclosing of localized cracks. The model uses homogenized parameters considering the weakness of the stone-mortar interface. It has the capability to use material pre-damage. The calculation determines the crack pattern induced in the bridge by support displacements and loads. The support displacement study consists of an inverse analysis aimed at determining the actual present state of the structure from the cracking pattern observed on the bridge. The methodology highlights the importance of considering the whole history of a masonry structure when assessing the current state.