An integrated approach for structural behavior characterization of the Gravina Bridge (Matera, Southern Italy)

An integrated geophysical approach using non-invasive, non-destructive, and cost-effective seismic and electromagnetic techniques has been implemented to recognize the static and dynamic properties (i.e. eigenfrequencies, equivalent viscous damping factors, and related modal shapes) of the Gravina Bridge and its interaction with foundation soils. The "Gravina" is a bow-string bridge located on outcropping calcarenites in the city of Matera (Southern Italy) and develops for 144 m along a steel-concrete deck. The foundation soil characteristics have been evaluated by means of three high-resolution geo-electrical tomographies, one Vs velocity profile, and two site amplification functions. The main structural characteristics of the bridge have been estimated through permanent and on-demand monitoring using seismic and electromagnetic sensing. The former consisted of accelerometers and velocimeters installed with different geometrical arrangements for permanent earthquake and on-demand ambient vibration test recordings. The electromagnetic sensing was realized by a microwave radar interferometer placed below the deck to measure the displacements of the whole scenario illuminated by the antenna beam providing a continuous mapping of the static and dynamic displacements of the entire target. Acquired data have been analyzed in both frequency and time-frequency domain with the aim to study the stationary and non-stationary response of the monitored bridge. These experimental campaigns allowed us to assess the robustness of the proposed approach and to set up the zero-time reference point of the bridge dynamic parameters.