A QUANTITATIVE RISK-BASED METHOD FOR PRIORITY ASSESSMENT OF EXISTING BRIDGES TO SEISMIC AND TRAFFIC HAZARDS

Bridges are key infrastructure of road networks and their closure due to miss-function or collapse could result in significant economic and societal losses. Many of the existing bridges in Italy, as well as in other European countries, are now older than 50 years and there have been many reports of bridge failures recently. Due to ageing, deterioration, existing damages, and inadequate maintenance, bridge structures may experience changes in condition, with respect to that at the time of construction. To address this concern, in Italy, multi-level and multi-hazard qualitative guidelines for risk evaluation of large-scale bridge portfolios were published in 2020. However, management entities are unable to create fine-grained priority ranking of bridges within a network due to the qualitative nature of the assessment approach. On the other hand, the majority of quantitative approaches that are available in the literature estimate the amount of risk in a variety of ways, exclusively taking into account either the data on seismic hazard or the assessment of the defects/damage condition alone. This study proposes a method for condition and risk evaluation of bridges considering general structural robustness and the presence of defects, simultaneously. The proposed approach uses numerical expressions to define risk and, thus, the priority of a bridge within a stock considering hazard, exposure, and vulnerability, and is applied to a case study of thirty real bridges in northern Italy, considering earthquakes and traffic loads as hazards. The findings are discussed from various perspectives, including the impact of defects on bridge vulnerability and priority ranking, according to two different defect state quantification strategies (average and critical). Finally, the results are compared with the current Italian bridge management guidelines.