Numerical Modeling and Dynamic testing on the Oglio Flyover of the new BreBeMi Highway in Italy

The Oglio flyover is one of three major flyovers belonging to the new BreBeMi highway in Northern Italy. The flyover consists of two separate ways, each of which made of hollow core prestressed elements with unbounded tendons, supported by hollow core circular piers. Friction pendulum isolators are used at the supports to disconnect the deck from the piles as for seismic actions. The finite element model implemented for the dynamic analyses of the Oglio flyover was developed using the commercial structural analysis software MidasGen. The 3D model of the whole deck was implemented using a refined mesh of shell elements to reproduce the longitudinal variations in the geometry of the cross section, the mass distribution, the fraction of dead loads and finishing actually in place during the dynamic tests in the most accurate possible way. Friction pendulum isolators were modelled implementing into the software the actual elasto-plastic behaviour curve provided by the producers, in order to take into account the different actual lateral stiffness of each isolator, depending on its vertical load. A linear modal analysis was carried out in order to obtain the numerical eigenvalues and eigenvectors, to be compared with the experimental values, derived from the operational modal analysis carried out on the flyover. The comparison in terms of frequencies and mode shapes was successful, yielding very good correlation for a significant number of modes. A model tuning procedure is currently being carried out in order to obtain a fully validated benchmark numerical model to be used for predictive purposes.