Seismic assessment of concrete balanced-system bridges

Concrete balanced-system bridges have recently become an object of interest, especially after the collapse of the Polcevera viaduct (Genoa, Italy), also known as “Morandi bridge”, occurred on August 2018 due to currently unknown reasons. Given that several other structures of this type have been erected in earthquake-prone areas, this work focuses on the numerical assessment of their dynamic and seismic response, taking the balance system of the Morandi bridge as a reference. First, nonlinear dynamic analyses were performed using triaxial records compatible with the local seismic hazard, also enabling the estimation of the seismic demand on the different bridge components. Then, since shear mechanisms in some of the members appeared to play a critical role in the seismic assessment of the considered bridge system, their capacity is assessed using both seismic code formulae and more advanced numerical procedures, including the Modified Compression Field Theory.