GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 2.3 323 Thepresenceof theelastomericsupportsonabutmentsandpier typicallyresulted indecoupling of the dynamic response of the bridge. EMA modes collected in Fig. 1d can be in fact grouped into two classes, namely vibration modes corresponding to (almost) rigid-body deformation of the deck and vibration modes associated with vertical flexural/torsional deformation of the deck. The first class includes EMA Modes 2, 4 and 5, which correspond to a rigid transverse (3.05 Hz), longitudinal (3.61 Hz) and torsional (4.83 Hz) modes, respectively. Concerning the other modes, Mode 1 has a natural frequency of 2.02 Hz and corresponds to the fundamental bending mode of a two-span beam. In it, torsional effects of the deck are almost null and the vertical modal components evaluated on a pair of transversally aligned points differ from each other by about 10%. The two spans show in-phase vibrations in Mode 3 (3.18 Hz), with spatial shape comparable to the second bending mode of a simply supported continuous two-span beam. A loss of symmetry in the longitudinal direction emerged in this mode, with amplitude of vibration at mid-span of Dogna side which is about 20% larger than the corresponding amplitude Fig. 3 – Numerical simulations: a) overview of 3D FE-model; b) reference model for the solution of the eigenvalue problem (3D-REF); c) 2D FE-model, cross-section on the pier; d) 2D FE-model, correlation with static truck-load experiments (flexural load scheme; longitudinal cross-section of the deck); e) example of a group of accelerometers.