Multi-source structural identification of undocumented historic bridges via 360°photogrammetry, operational modal analysis, and model updating

This paper presents a robust, ultra-low-cost, and fully non-invasive framework for the structural identification of undocumented and hard-to-reach historic bridges under severe data-scarcity conditions. The proposed methodology combines: (i) tethered spherical (360°) photogrammetry for metrically reliable geometric reconstruction, (ii) Ambient Vibration Testing (AVT) for experimental dynamic identification, and (iii) a two-stage finite element model updating procedure encompassing expert-guided boundary-condition refinement followed by automated material parameter calibration. The workflow is demonstrated on the Puente del Tranvía (Pinos Puente, Granada, Spain), a riveted metallic truss bridge lacking archival documentation and affected by severe accessibility constraints. Starting exclusively from data acquired through a rope-suspended (Formula presented.) camera, the proposed workflow enables the generation of detailed geometric blueprints and a mechanically consistent calibrated FE model. The updated model achieves frequency discrepancies below (Formula presented.) and Modal Assurance Criterion (MAC) values exceeding 0.90 with respect to the experimentally identified modes. The results demonstrate that the proposed approach can significantly enhance the structural knowledge level of inaccessible bridges while minimising inspection costs, operational complexity, and human exposure risks.