A tale of two bridges: half joint failure and deterioration processes

Load capacity assessment of deteriorating RC structures is a part of the strategy to avoid dramatic failures. Two cases of bridge collapse related to deteriorated half joints are presented. The structures were geographically distant – the de la Concorde overpass in Canada and the Annone overpass in Italy - but their histories show common features. The paper builds on the information gathered in the forensic investigations to explore the possiblities of load capacity assessment through different levels of data collection and modelling sophistication. Knowledge is gained by the comparison of half joints failure, design and construction errors, visible symptoms of damage, lack of maintenance, interventions carried out without taking care of overall conditions and lack of a bridge management strategy. Both structures were affected by shear design deficiencies. Regarding the deterioration processes, frost damage was the main issue in the North American case, while corrosion was the driving cause of the collapse in the European one. As for specific aspects, the de la Concorde overpass was influenced by the presence of a weakness zone resulting from inappropriate shear reinforcement details, further exacerbated by the poor concrete quality and severe exposure conditions. The structure in Annone was characterized by cracking caused by overloading and corrosion of the half joint reinforcement. The possibility to apply models within the assessment framework is discussed, with a focus on simple models for different levels of analysis.