Structural Aspects of the Collapse of a RC Half-Joint Bridge: Case of the Annone Overpass

This paper presents the technical causes of the collapse of the Annone overpass, a reinforced concrete half-joint bridge built in the early 1960s in northern Italy, occurred in October 2016. This work provides a detailed description of the geometry of the bridge and its conceptual design, highlighting the differences between the original design and the as-built situation. The condition of the bridge before the collapse and the event that triggered the collapse are also described. The paper highlights the critical issues occurring concurrently with the passage of a heavy truck. After a brief presentation concerning the characterization of the materials (concrete and steel), the work presents strut-and-tie models for the estimation of the ultimate capacity of the half-joints, which are considered to be the critical point of the entire structure. The strut-and-tie models are validated through comparison with experimental data obtained by testing a half-joint extracted directly from the bridge after collapse. The structural behavior of the bridge, the assessment of its safety, and the reasons that led to the collapse of the structure are also discussed through the use of simplified linear elastic and nonlinear finite-element models. Some weak points of the national infrastructural managing system, mainly referring to exceptional transports, are also discussed. The study highlights the methods that could be used to prevent future accidents in the absence of macrodesign mistakes and the main lessons learnt.