A Case-Study of Seismic Capacity Assessment of Railway Masonry Arch Bridge

Many existing numerical analyses determine the collapse state of masonry arch structures by assuming the formation of a hinge mechanism without sliding. This assumption can involve an overestimation of the load carrying capacity of the structure and should be carefully checked. In this work, the load carrying capacity assessment of a real railway masonry arch bridge is conducted through a fast numerical tool. The proposed numerical analyses determine the maximum seismic acceleration that the masonry structure can withstand in the presence of the traffic load prescribed by design codes. The results provided by the adopted tool show that the collapse mechanism contains not only hinges (relative rotations of adjacent blocks) but also sliding of blocks. In order to reduce the seismic vulnerability of the masonry structure, the effectiveness of possible interventions of reinforcement is then investigated with the tool. A classic intervention of rehabilitation is the application of an externally bonded reinforcement (EBR), such as fiber-reinforced plastics, on the surface of masonry. EBR is not effective in this case-study, as the collapse mechanism is dominated by an inter-block sliding movement that can not be prevented by the EBR. The adopted numerical tool identifies the correct collapse mechanism and avoids the economic cost due to the application of a useless EBR intervention of reinforcement. Further studies are necessary to evaluate if the filling material over the arch and the earth pressure on the piers can avoid the formation of mechanisms containing inter-block frictional sliding, which largely decreases the load carrying capacity of the arch bridge in the presence of seismic accelerations.