Critical review and modelling of the construction sequence and loading history of the collapsed Morandi bridge

The Viaduct over the Polcevera River, designed by Riccardo Morandi, was a very strategic and important bridge, built in Genoa (Italy) in the mid-60s. In addition to being a renowned engineering work, due to a very innovative design at that period, the bridge was also considered as one of the symbols of the city. On the 14th of August 2018, however, a portion of this bridge suffered a catastrophic sudden collapse that caused 43 casualties. In order to be able to understand, within the context of the necessary numerical forensic investigations, the stress state to which the bridge was subjected to at the moment of collapse, it is first necessary to reproduce both its construction sequence, as well as the loading history the structure was subjected to throughout its life. This work is thus focussed on such task, as well as on showing the differences between the construction sequence that had been initially envisaged at the design stage and the one that was then actually followed during construction. The analyses carried out highlight how important is the correct modelling of the construction sequence, showing how the use of unknowingly incorrect inputs, may give rise to erroneous stress state estimations, which can then in turn mislead post-collapse forensic studies. In addition, the changes in permanent loading (e.g. addition of asphalt layers, replacement of road barriers) and time-dependent effects (e.g. concrete creep and prestress relaxation) over the course of the 51 years of life of the structure, are also scrutinised and discussed, with a view to try to reproduce as accurately as possible the stress state conditions of the structure at the time of its failure.