PSI - Issue 84

Domenico Liberatore et al. / Procedia Structural Integrity 84 (2026) 1151–1158

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1. Introduction The city of Rome is rich of structures and infrastructures with prominent historical and artistic value which shall be preserved over time. Among these constructions, the ancient Roman bridges over the Tiber River are important monuments of cultural heritage and are witnesses of the complex Roman ancient construction techniques. Moreover, some of these bridges are still in use, primarily for pedestrian traffic. As an example, Pons Fabricius, the subject of this study, represents one of the most beautifully preserved, and is still nowadays used, as it constitutes one of the connections between the mainland and Tiber Island. Built using masonry as main structural material, like most of the ancient Roman constructions that belong to the Campus Martius historical area, the conservation of these structures requires particular attention, in order to preserve and enhance the historical building heritage of the city. The Capitoline Authority is responsible for the management and conservation of the archaeological sites of the city of Rome, which is a task that involves both architects and engineers, among other important technical figures, in a constantly conjunct work. Nowadays, the diagnosis of the actual conditions of historical buildings relies on innovative non-invasive methodologies, which allow to obtain efficient and accurate results with non-destructive tests without compromising the structural integrity. In this framework, Structural Health Monitoring (SHM) allows a continuous evaluation of the dynamic behavior of the structure, identifying possible structural issues and helping in the decision-making of maintenance plans. By controlling the health of these structures through the evaluation of the structural response to ambient vibrations, it is possible to improve their resilience, i.e. the immediate loss of capacity at the time of a certain event and the subsequent recover of the initial functions (Limongelli 2019). Sensors such as velocimeters and accelerometers are usually employed during structural monitoring, and their correct installation can affect the tidiness of the results. The analysis of the ambient seismic noise, also defined as microtremors, applies these sensors to the study of low-amplitude ground vibrations generated by natural sources, such as wind and meteorological phenomena, and anthropic activities, such as traffic, typically characterized by frequencies in the ranges of 0.2 to 0.5 Hz and 1 to 2 Hz, respectively. Operational Modal Analysis (OMA) is a tool for the identification of the dynamic characteristics of the structure through the acquisition and processing of ambient vibrations, aiming at obtaining eigenfrequencies and eigenmodes of the analyzed structure. The advantage of this technique is that no artificial external excitations are needed, limiting its invasiveness on the structure. White noise is, in fact, assumed as external input, with a random spatial distribution of the applied forces (Brincker et al. 2001). The characteristics of the bridge under examination, Pons Fabricius, are investigated first through a 3D laser scanner survey, to accurately and rapidly measure the position of a large number of points of the real structure, and through vibration measurements employing a Tromino®. The eigenfrequencies and eigenmodes are determined according to OMA. A finite element (FE) model of the bridge is then developed, taking into account the different materials used for the vaulted structures, spandrels, parapets and fill. The model is firstly analyzed in the linear range, determining its eigenfrequencies and eigenmodes, and comparing them with the results of OMA to validate the simulation. Then, the nonlinear behavior of the bridge under seismic actions is investigated by pushover analysis, using a FE model with constitutive relation characterized by material damage caused by tensile strains. The usual engineering demand parameters (EDP) are determined, along with the evolution of damage by means of damage indices and maps. 2. Pons Fabricius Tiber Island, located on Tiber River, was one of the first landing sites and became an important spot around which the first civilizations developed before the foundation of the city of Rome. Consequently, connections between the banksides and the Island were fundamental. At first, footbridges were installed, which later developed to small wood bridges to stone bridges. A brief history of Pons Fabricium, which connects the Island to the left bankside, is here given (Guarneri 2021, Inglese 2020, websites). The bridge was built in 62 B.C. by Lucius Fabricius, a curator viarum (curator of roads) during the Roman Republic, as indicated in the four inscriptions on the arches, and is still nowadays, after more than two thousand years, the only bridge over Tiber River to have survived almost entirely in its original structure, save for some improvements and restorations. It was built to replace a wood structure already existing in 192 B.C., but few years after its