Failure analysis of the impact of a falling object on a bridge deck

Even if not explicitly considered in most structural design codes, nor studied in-depth in past literature, reports from all over the world seem to indicate that accidental dropping of large heavy objects from transportation trucks can occur. The impact of such heavy objects onto the deck of a bridge can potentially give rise to the development of internal forces higher than those for which the bridge was designed to. To this end, the assessment of the response of bridges subjected to potential impacts from falling objects should be undertaken through idoneous numerical modelling. In recent years, the Applied Element Method (AEM) has been extensively employed to explicitly model complete structural response from the initial elastic stage all the way up to collapse and ensuing debris distribution. The present study, therefore, explores the capability of the AEM to model impact scenarios on bridge decks. It starts with a validation against experimental data available in the literature, and then passes onto the modelling of a case-study, the Morandi bridge, which at the time of its collapse, in August 2018, was being crossed by a truck carrying a heavy steel coil. However, initially use is also made of simplified analytical expressions available in the literature to estimate the forces generated by an impact of this type, with a view to gain additional confidence and reassurance on the obtained numerical results. A local model of the bridge span that the steel coil could have impacted is first developed to preliminarily assess different potential impact scenarios, followed by the analysis of a full model of the collapsed viaduct, including the estimation of debris distribution.