Optimization of the Number of Accelerometer Placements for Dynamic Identification of a Historical Masonry Bridge

Dynamic identification using accelerometers is a common technique for measuring the modal frequencies of existing structures. Strategically placing these sensors on a bridge allows for the derivation of its modal parameters through operational modal analysis (OMA). This study aims to demonstrate how the number of accelerometers required for the identification of a historical three-arch masonry bridge can be optimized. The experimental campaign involved the Santa Teresa bridge (STb) in Bitonto, a XIX masonry bridge in Southern Italy. Twenty-eight accelerometers were installed on the STb; frequency analysis was first performed with all accelerometers, and then the number was decreased to 13, 8 and 4 accelerometers. The four optimizations performed involved both the number and positioning of accelerometers along the central arch. The five primary vibration modes obtained revealed that with a smaller number of accelerometers, it is possible to correctly identify the natural frequencies of the bridge. A further optimization was per-formed with only No. 6 accelerometers on the keystone of the bridge’s three arches. The results of the modal shapes and natural frequencies showed that a limited number of accelerometers is sufficient to dynamically identify a bridge. The configuration with 13 accelerometers proved to be the best for this purpose. However, optimization with 6 accelerometers proved to be the best for recording normalized displacements compared to the reference configuration. The advantages of this study are directly related to the reduction in time, logistics and costs of in situ monitoring. This preliminary assessment approach enables the establishment of baseline conditions for subsequent periodic monitoring campaigns.