Fragility of existing Italian bridges to traffic loads

Fragility curves are a well-established tool to define probabilistically the vulnerability of an asset to a prescribed hazard. The majority of previous studies have investigated the seismic fragility of structures and infrastructures. Nonetheless, recent disasters have highlighted the need to assess the vulnerability of aging bridges to gravity loads. Based on existing data from the literature and novel data from some real case studies, the present work presents analytical fragility curves of Italian bridges to traffic loads. The class of simply supported, beam-type, prestressed concrete bridges constructed between 1960 and 1980 was considered, given that those structures are the most recurrent type of existing Italian bridges. Then, a fragility analysis was performed through a fully automated procedure implemented in MATLAB. Geometric, material and load parameters were defined as random variables considering their probability distribution and correlation through either univariate or multivariate models. Structural fragility was evaluated with respect to the limit state of collapse. The output of this study can be of interest to engineers and decisions makers who must manage existing bridges, considering their probability of collapse under traffic loads and eventually limiting their use before structural retrofitting.