PSI - Issue 84

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

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construction it was damaged by two massive floods, in 23 and 22 B.C. It was then restored in 21 B.C. by Marcus Lollius and Quintus Aemilius Lepidus, as written in two inscriptions on the arches. The bridge was then subjected to minor restorations in 1400s, consolidation interventions were made in 1679, and again in 1875 after an intervention of regularization of the water flux between the two sides of Tiber Island. A last restoration was made in 2000. The bridge has two segmental arches and a smaller arch in the central pier to facilitate the flow of water in the event of flooding, as shown in Fig. 1. The opening of the arch on the side of Tiber Island is equal to 24.97 m, while that on the bankside is equal to 25.93 m. The opening of the smaller arch is equal to 5.92 m. The centers of the two circumferences which approximate the arches have a height difference equal to approximately 0.50 m. The total length of the bridge is equal to 62.97 m and its total width is 6.30 m. The central pier is 12.50 m long and 20 m wide and is posed on a tuff basement. A triangular launching nose was built upstream, while a circular one was built downstream, to facilitate the water flow. The piers and the abutments are made of peperino and tuff blocks; the vaulted structures and the intrados of the arches are made of Gabine stone, while the crowning cornices and some claddings are made of travertine (Inglese 2020). During the restoration work for the Jubilee of 2000, the presence of opus caementicium in the internal structure was confirmed. Moreover, the external brick cladding dates back to additional restoration works carried out after the original construction.

Fig. 1. Pons Fabricius. (a) upstream side; (b) downstream side.

3. Laser scanner and ambient vibration survey 3.1. Laser scanner survey

The geometry of the bridge is captured through a laser scanner survey, obtaining a cloud of millions of points. The main challenges encountered during the acquisition of the cloud of points were related to the geometric configuration and topographic characteristics of the bridge. Specifically, the measurements could not be performed on the central pier and at the intrados of the two arches due to the presence of the river. As a result, some supports on Tiber Island and along the Tiber riverbank were exploited, in order to ensure complete coverage of the structure and a sufficient

Fig. 2. Cloud of points of Pons Fabricius extracted from the laser scanner survey (a); ambient vibration testing equipment, Tromino®, 2025 (b).