Attention Classes and Seismic Vulnerability of Highway Bridges

This study compares different methodologies for assessing the seismic vulnerability of viaducts, focusing on the contrast between the 2003 Ordinance procedure (OPCM 3274/2003), in particular on modal pushover analysis, and the more recent 2022 National Guidelines (CSLLPP (2020) D.M. 204/2022) for existing bridges. Results, expressed in terms of return periods, are evaluated against the 949‑year benchmark for the life‑safety limit state (Chopra & Goel, 2002, 2004; Paraskeva & Kappos, 2008). The analysis also examines the multi‑level structure of the Guidelines, particularly Level 2 and the attribution of Attention Classes (MIT–CSLLPP, 2020). A case study and a statistical evaluation of 382 viaducts reveal weak correlation between the qualitative classifications of the Guidelines and the quantitative seismic assessments derived from the Ordinance methodology. Findings highlight the importance of adequately capturing pier behavior and show that several bridges has not been assigned a HIGH overall Attention Class nonetheless they fail seismic checks. The results indicate that quantitative seismic analyses can effectively serve as an equivalent to Level 4 of the Guidelines, revealing that many structures currently exempt from verification are not seismically compliant, an insight crucial for informed prioritization of interventions.