GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 2.3 321 frequency. The mechanical exciter, capable of generating forces with maximum amplitude up to 20 kN, was mounted on the bridge deck at one third of the span on Dogna side, close to the downstream sidewalk (Fig. 2a). The acceleration response of the bridge was measured by seismic accelerometers (ICP Series 393B12) with sensitivity equal to 10 V/g. During the tests, the rotating frequency of the actuator was gradually increased in the ranges 1-6 Hz and 6-15 Hz. A data acquisition unit was used for data acquisition, control of the force actuator and automated signal processing. Structural response was simultaneously measured by 18 sensors (16 placed on the bridge deck and 2 on the top section). 8 accelerometers with vertical axis were mounted on both the sides of the deck, e.g. at the quarters of the right span (side Dogna), and at mid-span of both the spans. Longitudinal and transverse motions were monitored at the mid-span cross-section of both spans (Fig. 2a). Based on the experimental layout proposed in Fig. 2a, the response of the structure was separately measured under excitation parallel to the vertical (V), longitudinal (L) and transverse (T) direction. Tests were carried out in absence of the deck asphalt layer. FRF measurements were carried out with a frequency increment of 0.05 Hz. A smaller step (0.02 Hz) was used in the bands 1.8-3.4 Hz and 6.5-8.5 Hz, to improve the identification of vibration modes under vertical excitation. Fig. 2 – Dynamic experiments: a) instrumental layout; b) example of comparison between measured and synthesized point inertance; c) identification of EMAModes 6 and 7; d) 3D view of experimental modal shapes.