PSI - Issue 84

Michela Briganti Botta et al. / Procedia Structural Integrity 84 (2026) 344–351

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The parts that make up a masonry bridge are as follows: • the arch, which is the structure that carries the walkable deck, • the supporting structures for the arches (abutments and piers), • the foundation structures, • elements that seem to have no structural effectiveness, placed above the arch to provide a flat, walkable surface (spandrel, infill cap), • the infill is contained laterally by two walls (timpani or front walls) placed on the outer side of the arch.

Fig. 1. Masonry bridge

Most of these structures today require two categories of intervention related to the most common issues encountered in existing bridges: waterproofing problems and the lack of adequate space for walkways intended for maintenance work. These issues are currently of crucial importance in terms of safety: a piece of infrastructure must guarantee its functionality over time, and it is essential to minimize the physical degradation of the materials that make it up. At the same time, it is necessary to ensure safe access for specialized staff for all maintenance, inspection, and control activities. 1.1. Lack of Waterproofing The capping on historical bridges is often no longer capable of performing its role of waterproofing the arch structure from water infiltrating from the deck. Water infiltration problems in masonry arch bridges are mainly caused by the erosion of mortar joints, which create preferential paths for water, leading to further degradation and settlement. Water, especially if it contains salts, can seep into the fill and wash out the masonry, leaving moisture stains and causing surface disintegration. The infiltrated water can cause freeze-thaw cycles: it can damage the blocks and accelerating wear and exfoliation, weakening the structure over time. This process can increase pressure on the piers, leading to cracking, bulging, and, in the worst cases, collapse, requiring urgent intervention or closure of the bridge. The effects of infiltration can be prevented at the source by adopting water protection systems, such as waterproofing the surfaces. 1.2. Lack of Sidewalks The deck of a masonry arch bridge can seat one or more railway tracks and is generally characterized by a cross section that does not allow for safe passage of personnel conducting maintenance or inspections. Periodic inspections of bridges are imposed and are aimed at assessing their safety and conservation status. These inspections, ranging from the initial inventory to more in-depth checks, must be carried out regularly by qualified personnel who must be able to safely access the deck. Therefore, it is necessary to ensure the presence of a service walkway according to the standards outlined in the RFI design manual. In most cases, the walkway cannot be built inside the deck because historical structures do not have enough space.