Numerical Assessment of the Seismic Vulnerability of Bridges within the Italian Road Network

The safety of existing bridges represents a serious problem in Italy since these structures are fundamental for the national transportation system and, at the same time, can be subject to significant deterioration phenomena linked to the fact that the construction period typically dates back to the 1960s. This study involves the seismic analysis of five case study bridges belonging to the Italian Road Network. Using nonlinear time–history analysis with sets of code-spectrum compatible ground motions, analytical fragility curves have been constructed for each of the five bridges. The results obtained interpreting the analytical fragility curves agree with the fact that the seismic behavior of existing bridges can be problematic and that higher seismicity can be associated with more detrimental behavior. In particular, the results reveal that in regions with higher seismicity, the main problems in bridges are related to bearings and connecting elements located in the piers. Five case studies have also been analyzed to determine the Structural and Foundational Class of Attention and Seismic Class of Attention, following the approach proposed by the 2020 Italian Guidelines. In this way, it is possible to compare two different assessment approaches with different safety levels. The results obtained with the two approaches are in good agreement considering bridges in high seismicity regions, while the procedure of the Guidelines could lead to not reflecting the seismic behavior of bridges when the seismicity of the area is lower.