GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 2.2 369 sensors were placed directly above the road, it was necessary to close the bridge to traffic. Overall, a set of 6 monitoring sites were placed in both edges of the road segment as reported in Fig. 1a. At each node were employed both a 3-axial velocimeters (Nanometrics Trillium Horizon 20s) and 3-axial accelerometers (Nanometric Titan). All the sensors were aligned in the same direction so that the two horizontal components coincide with the longitudinal and transversal directions of the bridge (Fig. 1a). The tests consisted in the passage of a fully loaded vehicle at increasing velocity (20 km/h, 50 km/h and 80 km/h); the passage of a fully loaded vehicle, in an almost static way, over an obstacle of increasing thickness (2.5 cm, 5 cm, 9 cm) about 23 m from the column 4; the passage of a fully loaded vehicle at increasing velocity (20 km/h, 50 km/h, 60 km/h) braking at the centre of the span. As an example, we report the amplitude spectra of the signals triggered by the braking truck at 50 km/h speed over the monitored bridge segment (Fig. 3c). The spectra highlight differences between the components either in the frequencies and in the amplitudes which are ascribable to the mode of vibrations of the bridge. Conclusions. The tests carried out at S. Paolo bridge are of extreme importance. In fact, with reference to road bridges of significant importance, dynamic load tests are mandatory in addition to static ones (NTC 2018). Dynamic monitoring consists in the processing of data detected by control instrumentation in response to dynamic disturbances present on the Fig. 3 - Comparison of the waveforms of a Mw 4.3 (20-01-2022 09:19:57) at 166 km recorded at S. Paolo bridge recorded with a Trillium PH 120 s located at ground surface (a) and recorded with an identical sensor placed at 51 m depth (b). Amplitude spectra for the three components of one of the velocimeters placed over the viaduct (c, see text for further information).