GNGTS 2014 - Atti del 33° Convegno Nazionale

320 GNGTS 2014 S essione 2.3 FE-model is developed and FE model updating is carried out to reduce discrepancies between analytical and experimental dynamic estimations. The seismic behavior of the bridge is then predicted using suitable ground motion records and an optimized, computationally efficient, 2D FE-model that could represent the baseline model for future monitoring and condition assessment programs on Dogna bridge. The Dogna Bridge. Dogna Bridge is a two span, two-lane post-tensioned reinforced concrete (RC) bridge. Construction of the bridge, designed in accordance with NTC2008, was completed in Spring 2007. Main features and nominal dimensions are shown in Fig. 1a. Each span is 37.5 m long and a single RC pier (2.4 m thick, 4.0 m deep and 10 m high) is present at mid-span. Pier was built on cast-in-place concrete, 18 m long piles (diameter 1.2 m). The lateral abutments, consisting of vertical RC walls, are supported on 22 m long cast-in-place concrete micro-piles (diameter 0.3 m). At mid-span, the deck is continuous and simply supported – both on the abutments and on the pier – by two multi-directional elastomeric bearings (Fig. 1b). The bearings are seismic isolators (type SI-N-1200/112, FIP Industriale) with 1200 mm diameter, made up of layers of steel laminates and hot-vulcanized rubber. For large shear strain, their compound is characterized by nominal dynamic shear modulus G din = 0.8 MPa and equivalent viscous damping coefficient ξ = 10-15%. The bridge cross section is uniform along the longitudinal direction, except near the pier. The typical cross-section consists of a 5.0 m × 1.3 m central rectangle, which contains the prestressing tendons, and two lateral portions with thickness varying from 0.5 m to 0.2 m. Near the pier, the thickness of the deck cross-section gradually increases from 1.3 m to 2.2 m (Fig. 1a). Dynamic testing. In May 2007 the bridge underwent an extensive series of harmonic forced vibration tests with low levels of excitation for determining the frequency response function (FRF). Steady-state harmonic vibrations were induced by means of the stepped-sine technique. Aunidirectional mechanical actuator with out-of-balance rotating masses furnished a sinusoidal load acting along a given direction and with amplitude proportional to the square rotating Fig. 1 – Dogna bridge: a) plan, elevation and transversal cross-sections (on the pier and at the centre of a single span); b) seismic isolators: cross-section, overview and nominal characteristic behavior.