Operational modal analysis for structural identification of reinforced concrete bridges: two case studies

The assessment of existing bridges requires diagnostic methods capable of identifying structural characteristics without interfering with normal service conditions. Operational Modal Analysis (OMA) represents a powerful technique for this purpose, as it allows the dynamic properties of structures to be extracted from ambient excitation sources such as traffic and environmental vibrations. This paper presents two applications of OMA to reinforced concrete bridge structures located in southern Sardinia, Italy. The first case study concerns a prestressed concrete viaduct composed of multiple simply supported box girders, while the second investigates two arch-stayed reinforced concrete bridges with identical geometry. Accelerometric measurements were acquired under operational conditions and processed using frequency-domain techniques to determine the fundamental natural frequencies of the structures. The experimental results were compared with numerical predictions obtained through finite element modeling. The comparison demonstrates a satisfactory agreement between measured and simulated modal properties, confirming the reliability of the adopted monitoring strategy. The presented approach highlights the potential of operational modal analysis as a practical tool for structural identification and long-term monitoring of existing bridge infrastructure.