Safety assessment of existing post-war reinforced concrete bridges. The case study of ‘Gerber girders' bridges in Italy

The interest in the structural maintenance design of existing bridges of the Italian road network is nowadays growing, due to the need to overcome structural inadequacies and/or degradation phenomena. In this framework, the new "Guide-lines for risk management, safety assessment and monitoring of existing bridges" outline the required procedures and tools, identifying the most critical issues of the different bridges’ structural typologies, including Gerber girders in reinforced concrete bridges. A safety assessment of Gerber bridges is thus mandatory as for the presence of joints which do not comply with current design practice and codes as for the occurrence of aging-related decay phenomena, e.g. due to water infiltration. In this context, a novel cross-disciplinary procedure for the assessment of Gerber bridges is here presented, giving an insight on the so-called ‘knowledge phase’. Firstly, the paper analyses the introduction and diffusion of this structural typology in Italy, giving a classification of existing Gerber bridges and focusing on their recurrent degradation phenomena. Finally, a discussion on historical sources which can be used to draw useful information, e.g. construction history surveys, archival drawings, calculation manuals and codes, is presented.