Vulnerability to traffic loads of typical Italian bridges in relation to the evolution of the code framework

Over the last century, the definition of the design traffic loads for Italian road bridges has undergone a continuous evolution, starting from the first code in 1933 up to the current code. The changes in the arrangement and in the intensity of the design loads that have occurred over the years resulted in significant variations, both decreasing and increasing the overall static demand required to the bridges compared to previous codes. As part of a broader study on the structural risk of existing bridges with respect to traffic loads, it is certainly of interest to investigate the influence of the adopted design code on the risk itself. The paper presents some of the results of a study conducted with this purpose, regarding Prestressed Concrete beam-and slab bridges with simply supported spans, one of the most common typology among bridges with medium-small span. The comparison between historical codes and current one is carried out in terms of internal forces of the most stressed girder, taking into account the transverse distribution of loads. The study can provide useful elements for the definition of a fast procedure for the preliminary assessment of typical existing Italian bridges based on the geometric characteristics of the decks and their design age.