Essential dynamic characterization of a historical bridge: integrated experimental and numerical investigations

This paper reports on a series of experimental tests and a numerical study carried out on the historic masonry bridge of Santa Teresa of Bitonto, located in Bari (Southern Italy). A systematic working technique was planned and carried out with the final objective of defining the dynamic properties of the bridge and verifying the seismic repose by means of a response spectrum analysis. Initial stages were carried out including historical research, visual inspection, and geometric integrated aerial and ground survey on-site using UAV technique for the identification of the geometric details of the structural and non-structural elements of the bridge. An experimental campaign was scheduled and executed by performing free and forced-vibration tests using uniaxial and biaxial accelerometers placed at 22 monitoring points to retrieve the main vibration modes of the bridge with their corresponding frequencies and damping ratios. Although the free vibration tests detected only the main mode of vibration due to the squat nature of the structure, the forced-vibration tests help to confirm the findings and identify further modes of vibration. The consistency of the experimental frequencies was statistically confirmed by varying the conditions of the forced-vibration tests. A Finite-Element (FE) model was constructed and calibrated qualitatively (i.e., order of vibration modes) with respect to the experimental ones, based on both the geometric survey and the visual inspection outputs. Then, a second phase of calibration was undertaken by tuning the remaining free parameters to match the numerical values of all the detected modes. The calibrated model, capable of producing the experimental results, was adopted for performing a response spectrum analysis for the global response evaluation of the bridge. The results showed a globally acceptable level of stress, while excessive values were limitedly observed in a few critical zones.