The oblique bridges in Italy

With the development of the railway system since 1861, also in Italy appear the arch brickwork bridges, called oblique bridges. These particular buildings had to allow the railway platform crossing of the rivers arranged obliquely in comparison with the rail’s direction. They obtained this with the realization of barrel vaults, but their development wasn’t perpendicular to the plane containing the frontal arches. The arch’s mechanics scholars coined in this way the concept of the void-thrust to represent a phenomenon apparently contradictory, that was anyway resolved in the structural way. The existence of these thrusts was postulated since the first treatises about oblique bridges of the end of XVIII century. Since that moment the solution of the problem of void-thrust was resolved improving the building device, but this brings up for discussion again an essential hypothesis of the mechanics or rather the irrelevance of the building device for the stability of the vaulted structures. The event of the oblique bridges is the swansong of the stereotomy and of the modern brickwork. In this case theory and practice of the construction sustain theirself, and the final solution to warrant the safety is a pragmatic one. Today the rehabilitation of these structures involves many technical and scientific questions. Besides the increase of the load that rests on then because of the augmented weight of the trains and the material’s deterioration, others factors complicate a complete rehabilitation of these constructions, like the difficult comprehension of the total brickwork construction. The present work wants to offer a contribution to the description and to the knowledge of italian oblique bridges through the analysis of the italian treatises; then is useful studying more minutely the construction of the vault: building device, materials and other technical aspect. We think that is essential to define better the total structural features.