Structural safety assessment of existing cantilever bridge deck stocks with half-joints through fragility curves

The increasing traffic loads and the simultaneous aging of the European infrastructure network are determining the need to carry out safety assessments for a growing number of bridges. Prestressed concrete (PC) cantilever decks are particularly common, especially for overpasses, as they were widely constructed in the 1960s and 1970s. This study assesses the structural safety conditions of such decks, drawing on a comprehensive experimental campaign conducted on two stocks of PC highway overpasses with Gerber half-joints, comprising seven (the first) and eleven (the second) structures, respectively, built in southern Italy in the 1970s. The experimental data collected have been analysed statistically to derive probability distributions of key mechanical and physical parameters. Based on these distributions, multiple analytical simulations were conducted using the Monte Carlo method to account for inherent uncertainties of material, geometry and load parameters. Flexural and shear demands are calculated and compared with their capacity counterparts, by accounting for a broad range of potential collapse mechanisms. The primary result is the evolution of the probability of failure for each mechanism as traffic loads increase, represented by “fragility curves”. This methodology enables a rapid but accurate assessment of multiple similar bridge decks, allowing infrastructure management companies to quantify the stock’s safety level, identify critical failure mechanisms, and prioritize targeted strengthening interventions.